WEBVTT

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it's a rude awakening and mornig welcome
to do with the uh... third week of

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medical school for you you might have
noticed that our

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cohort of medical students has that
doubled

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in size if you guys have noticed you if
you're here first of all the job finding

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this other lecture hall sorry work

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jumping you from place to place but this
is part of

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trying to revamp

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all of our lecture halls and so we had
to do this in a stage process those of

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you that understands gantt charts

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and construction

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will uh... will sympathize but you found
the place

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in north lecture hall now are your
colleagues here and suits

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they are a great source of advice

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and uh... and uh... being able to and
sort of queries about different staff so

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now you've got your built-in

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counselors uh... here but they're also
going to be very busy as you notice they

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probably probably noticed they started
about an hour before you did so

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for

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that's what you have to look forward to
it here

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that that

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uh...

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hope you guys survived your first quiz
hopefully it wasn't too painful i know

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many people ask will they be medical
decision making

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stuff on the quiz and the answer to that
was

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uh...

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remember that genetics in pathology or
the big components of the quizzes and

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that we in india and we have assignments
so you turned in your first assignment

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last thursday at small groups

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uh... i'm in the process of reviewing
them

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they will get back to you in your mail
boxes

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uh... so you will be have them to study
from

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i will also when i return them to you
you should pay attention on c_ tools all

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publisher ultimate which will also have
the answer key

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to interview uh... assignments

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so there's no hidden doctors here it'll
be a turkey will give you an explanation

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to each of the questions that way you
can look at your answer what banter in

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turkey was any notes that you had

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and reconcile and if there are any

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other questions certainly we're here to
help you

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you have another small group tomorrow
afternoon

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that will largely be based on material
that we cover today

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uh... hopefully if you guys have had a
chance to get a jump start on that i try

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to post in a week in advance

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you're more then welcome to

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uh... reading ahead is hopefully fine
encouraged if you want to do want to

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that's totally fine as well

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there should be enough time to be able
to complete that again it's the same

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protocol

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bring it to your small group still
discuss that with here

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co students in your small group silkair
and then returned them

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uh... tournament and then i'll be
returning to you in a timely fashion

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any questions about the logistics of
this course for this part of this force

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so why don't we go ahead and get started

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uh...

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today we're going to be for we're gonna
be picking up a little bit where we left

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off

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last time

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and he wants start by declaring uh...
any industry relationships

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that i might add to contacts that meet
your otherwise

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in the answer is

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certain factor

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uh... dancers is i have not been

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to disclose

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so nothing that would uh... interfere
with my ability to present you an

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objective view of uh... medical decision
made

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so our first just returning to where we
left off with their first thread

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this is around information retrieval
focusing on asking in acquiring

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if you remember and

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after last monday we left off by talking
about the way the structure well

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foreground question and these are sort
of that

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uh... fundamental tools that were
required to

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af but good questions get the
information from the literature and then

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interpret and apply them as a way to
focus a little bit just to revisit

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this tool that we talked about

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this was the pico tool that encourage
you to just use it as a tool basically

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it's a way of specifying the different
elements in your question there will be

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important

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tour it ought to be able to sort out the
appropriate answers

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and we think it's important to be able
to do with in advance

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because by doing it in advance

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uh... you're really able to focus on
what you need and what your patients

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need

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so in order to practice doing this went
to ask you to do is to look at this case

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and practice with your partner

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jotting down the foreground

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uh... question so let me go over the
case real briefly

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because we're gonna be using this uh...
moving forward

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so this is now this is a forty
two-year-old woman

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who comes to her primary-care
practitioners office

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for follow-up of her diabetes and you're
the medical student

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she's currently on libby ride

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ten milligrams twice daily

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however her blood sugars still stay
elevated despite being on that

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medication delivery right

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after you see this patient

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you're attending asked whether you think

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she should admit foreman to her regimen

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pretend like you know what would your
ideas and pretend like you know what

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metformin is you may not but these are
both

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uh... it is that we use in diabetes

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we'll be right is the sole final you
react

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and metformin is uh... another agent
that we use

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uh... packets dvd

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uh... and i cant really pronounce what
that actually stands for it's a very

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difficult word to pronounce but

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suffice it to say good beer i can see
his your um... insulin

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uh... usa secretion but metformin
improves your sensitivity uh... to

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insulin is well or that your body makes

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so let's say you know all of that

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and the question i would ask you to do
is to start putting on

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your hat as if you were a clinician just
to get a sense of what

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these kind of foreground questions are
about remember therefore important

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components

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for a foreground question you have to
define the patient population that

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you're interested in

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you have to define the intervention

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that you're interested in

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the comparison group that would be part
of the study that might help you answer

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the question andy outcomes of interest

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that you would be that you in your
patient would be interested in

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this will help you then scanned the
literature to figure out what are the

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articles that would be most relevant

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for this particular case

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so i'd like you did it was turned your
partner and come up with one

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that would meet all four categories it's
a fairly straightforward exercise but

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wanna make sure that you get

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such answer practice that's so spent a
couple minutes doing that and we'll talk

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about it

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a

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okay three parking lot with remember
that really

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nobody answers here because

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every single uh... every single answer
that you would give each of the four

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different categories would have some
debate around

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whether the article that you retrieved
with those particular characteristics of

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the study population

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would actually help you answer your
question

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or not and the degree to which it would
do that so let's just hear some of the

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questions what i'd like you to do is not
the same like he was ex and i was

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uh... was why

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i'd like to see if you could stated in
the form of a question one that would

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contain all four

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of those different components

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just a little hint

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i might ask something like this uh... on
one of the either the assignments

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or certainly

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while our final examination as well so
who wants to take a stab at it

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them

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uh...

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okay great so here let me let me restate
this

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in women with diabetes

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what is the effect of metformin plus
glider ride

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blood sugar levels compared to drive me
right along

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so let's see if we got all the before
components in their is that patient was

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women with diabetes your intervention
was metformin it would be right together

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versus delivery right alone in the
outcome you're interested in

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was improvement in her blood sugar
levels okay

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so let's break that down the patient
population is that were women with

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diabetes was that it did anyone have
something different

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then women with diabetes here

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awesome al you specified in age cutoff
so women with diabetes over forty ok any

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other

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variabilities there

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asel na specifying gender so just all
patients with diabetes let's back up and

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think about that

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limelight it so that the question would
be if we're to get an article

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that had

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all ahead men and women

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in the past study population

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would we say that's ok to extrapolate
the results

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and then apply to this patient
population

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and so you said

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potentially that would be ok any reason
to think that verb rationale

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what goes through your mind as you're
making that call

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but the answer being that date one of
the rationale might be fifty-year

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defined studies where you have

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both genders represented as opposed to

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one gender alone so that's one certainly
one consideration what might be another

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consideration you would use

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uh... so now you're talking you're
getting even more specific saying

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impatience

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who are

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poorly controlled on good be ride with
diabetes

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what about the comparison group purses
uh... verses the intervention so that we

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another

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shape that you would be there

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but that you might use backing up to the
gender issue

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the question i would ask you to ask and
we ask this question all the time does

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the disease manifest differently or act
differently

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in one gender verses another

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does the disease manifest if really
inpatient over forty

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rice's those that might be younger than
forty

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those would be the questions that you
would be asking yourself and remember

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you have to build some background
knowledge about this subject before

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being able to ask the most sophisticated

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foreground question

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i'm trying to know a little bit about
the pathophysiology

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but it's reasonable to have those
different want uh... those those

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different shades of variation

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in the patient

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the intervention was metformin plus
we'll be right did anyone have a

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different intervention

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oddly be what we're thinking about the
kind that we're not talking about

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stopping the glitter ride and adding
metformin

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but in some cases you might be looking
for head to head comparison

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and in fact if you're thinking about it
from a drug company standpoint they may

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be interested in head to head
comparisons because they're trying to

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prove one

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at the at the efficacy of one drug over
another

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if you're thinking about it from the
standpoint of

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of uh... pathophysiology you might be
interested in head to head comparisons

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but if you're thinking about it in the
practical sense we often might be

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looking at

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adding and agent to an existing regimen

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those are less commonly found

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in the literature on just a tad

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and so you may be stuck saying well i
don't have an additional

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uh... i don't have a study that shows
the addition of metformin

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and so you would have to extrapolate

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from head to head comparison

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which is tricky did you

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certainly beyond the scope of this
course but keep in mind those of the

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questions that we entertain as positions
as for reading the literature

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now one of the outcomes that was was
mentioned was improvement in blood sugar

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so first of all how would we measure
that

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but voz votes

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okay so you could be looking at that's
the blood sugar which have been one

00:11:37.309 --> 00:11:40.075
marker of diabetes hemoglobin a one c
which alert next year

00:11:40.075 --> 00:11:45.013
is a eleven for a test that we get that
it looks at patients long-term control

00:11:45.013 --> 00:11:47.959
our blood sugar at least medium control
over the past three months

00:11:47.959 --> 00:11:49.048
so that be a good outcome

00:11:49.048 --> 00:11:53.017
to specify so you could get that level
of specificity and you might find

00:11:53.017 --> 00:11:57.369
studies that look at just after larger
verses does that look at a one c and you

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would have to decide which ones

00:11:59.066 --> 00:12:02.068
for me in my patient now would be
important consideration

00:12:02.068 --> 00:12:05.072
any other types of outcomes you guys
looked at

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or anyone specified besides blood sugar
improvement

00:12:15.027 --> 00:12:18.047
basil side effects might be another
outcome that you would look at what sort

00:12:18.047 --> 00:12:21.089
of side effects might be worth we'd be
worried about a few

00:12:21.089 --> 00:12:24.075
if you know any

00:12:24.075 --> 00:12:27.082
so one that i might be worried about is
would i be dropping this patient's blood

00:12:27.082 --> 00:12:29.059
sugar too low

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to the point that they have hypoglycemic
events

00:12:31.032 --> 00:12:32.097
so that would be something to be
thinking about

00:12:32.097 --> 00:12:37.031
but absolutely remember this is a
therapeutic question that your asking

00:12:37.031 --> 00:12:40.096
and as if they're peter question there
are unintended or sometimes

00:12:40.096 --> 00:12:44.419
uh... known side effects of the
different genes that we

00:12:44.419 --> 00:12:47.026
that we use and so looking at the
adverse events

00:12:47.026 --> 00:12:49.011
would be another important outcome

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so keep in mind this is just an exercise
but to wall

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to get us to where we dot where we need
to go so that when we look at the

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literature

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we know what we're looking at

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that is the point of the foreground
question

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now this is up there

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foreground question before i questions
about their feet

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later on in this lecture really talking
about or run questions

00:13:07.459 --> 00:13:09.061
as it pertains to diagnostic tests

00:13:09.061 --> 00:13:12.369
again to get distinct types of questions

00:13:12.369 --> 00:13:16.979
but both equally important here a couple
of examples that we that were uh... that

00:13:16.979 --> 00:13:21.029
would be reasonable i think you guys
came in kimba up with these in tight to

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die but if that was one thing we didn't
talk about the fact that this woman

00:13:23.098 --> 00:13:25.089
is a tight to diabetic

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she may be insulin requiring more
insulin

00:13:28.061 --> 00:13:32.001
resist uh... you know that we talk about
that one person so i can fight one being

00:13:32.001 --> 00:13:33.007
autoimmune

00:13:33.007 --> 00:13:36.019
more likely to happen upon early onset

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tight too

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uh... not necessarily requiring insulin

00:13:39.097 --> 00:13:42.589
uh... and so you might want to
distinguish that studies that you're

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looking at

00:13:43.066 --> 00:13:46.084
but then there's a question is metformin
good write better than the bread alone

00:13:46.084 --> 00:13:49.075
in lower bucks ordered that was
something that you guys came up with and

00:13:49.075 --> 00:13:52.076
here's the side-effect question among
women with type two diabetes

00:13:52.076 --> 00:13:56.017
are there more instances of low blood
sugar of insufficient on both metformin

00:13:56.017 --> 00:13:57.066
it would be right

00:13:57.066 --> 00:13:59.036
when compared with we'll be right along

00:13:59.036 --> 00:14:02.068
so that you guys came up with this
fairly straightforward exercised but

00:14:02.068 --> 00:14:06.036
keep in mind level of specificity is
important because you're gonna be faced

00:14:06.036 --> 00:14:08.011
with a ton of different studies

00:14:08.011 --> 00:14:10.087
you're gonna have to work through to
figure out which are the ones that are

00:14:10.087 --> 00:14:14.096
most relevant tumi and the patient that
you're working with what are the

00:14:14.096 --> 00:14:17.051
important outcomes to that may be very
different

00:14:17.051 --> 00:14:20.057
and the outcomes that you are interested
in and so it's important vehicle to

00:14:20.057 --> 00:14:23.053
specify that of prop yes

00:14:23.053 --> 00:14:25.379
went

00:14:25.379 --> 00:14:27.072
at

00:14:27.072 --> 00:14:31.899
so it literature doesn't exist uh...
what do you do that is probably

00:14:31.899 --> 00:14:35.032
uh... the hardest question we face as
clinicians

00:14:35.032 --> 00:14:38.008
there is a when i'm gonna ask you to i'm
not gonna be able to answer that

00:14:38.008 --> 00:14:39.003
completely

00:14:39.003 --> 00:14:42.099
but as we build our course over the next
three years what you're going to get a

00:14:42.099 --> 00:14:44.008
sense of

00:14:44.008 --> 00:14:46.076
is that there is a hierarchy of evidence

00:14:46.076 --> 00:14:48.028
meaning that as

00:14:48.028 --> 00:14:52.045
certain studies take on certain study
characteristics both in terms of how

00:14:52.045 --> 00:14:56.092
they're designed and how well their
implemented the level of evidence that

00:14:56.092 --> 00:14:59.086
they provide become stronger or weaker

00:14:59.086 --> 00:15:03.028
and so it's not necessarily do i have

00:15:03.028 --> 00:15:05.007
is there no studies out there

00:15:05.007 --> 00:15:07.098
what are their studies out there that
are less well done and so what do i do

00:15:07.098 --> 00:15:08.086
with those

00:15:08.086 --> 00:15:10.094
compared to studies that are really well
done

00:15:10.094 --> 00:15:14.061
keeping in mind that the studies that
are really well done are actually less

00:15:14.061 --> 00:15:15.899
frequently encounter

00:15:15.899 --> 00:15:19.079
and those studies that are not so well
done or studies that are

00:15:19.079 --> 00:15:21.082
observation as opposed to control
clinical trials

00:15:21.082 --> 00:15:24.043
so the answer your question is i don't
have the answer now but that is exactly

00:15:24.043 --> 00:15:26.007
going to be the point of the next three
years

00:15:26.007 --> 00:15:29.066
what do you do when you're faced with a
quandary we're gonna try to party

00:15:29.066 --> 00:15:31.073
conceptual model that will on full

00:15:31.073 --> 00:15:35.002
that you'll get more comfortable

00:15:35.002 --> 00:15:38.066
there many sources the foreground
questions these are the pics precise

00:15:38.066 --> 00:15:40.729
questions if you go to medline four

00:15:40.729 --> 00:15:43.091
or that you will go to a practice
guidelines or you'll use evidence-based

00:15:43.091 --> 00:15:46.139
databases and all of these sorts of

00:15:46.139 --> 00:15:48.008
of uh... of resources will be introduced
to you

00:15:48.008 --> 00:15:52.003
as we go through

00:15:52.003 --> 00:15:54.081
so building on those questions then

00:15:54.081 --> 00:15:58.879
we do need to then figure out what is
the data that we're getting and how do

00:15:58.879 --> 00:15:59.093
we interpret

00:15:59.093 --> 00:16:03.149
and so as i mentioned therapy types of
questions are

00:16:03.149 --> 00:16:04.088
are very important part

00:16:04.088 --> 00:16:07.019
of what we do is the nation's they seem
to be

00:16:07.019 --> 00:16:10.579
the most natural thing you would assume
positions do which is prescribed

00:16:10.579 --> 00:16:11.031
treatment

00:16:11.031 --> 00:16:12.088
and figure out whether it's

00:16:12.088 --> 00:16:14.043
making a difference or not

00:16:14.043 --> 00:16:17.092
however it is not the most fundamental
thing that we do in fact

00:16:17.092 --> 00:16:20.007
therapeutic questions are very
sophisticated questions

00:16:20.007 --> 00:16:24.239
that we actually don't cover much about
their pete this year

00:16:24.239 --> 00:16:27.084
we do it in your second year as you
start tackling pathophysiology

00:16:27.084 --> 00:16:29.003
this year

00:16:29.003 --> 00:16:31.008
the question we want you to start
thinking about

00:16:31.008 --> 00:16:33.072
what is going on

00:16:33.072 --> 00:16:39.023
is that you all a g of why what i'm so
the the clinical manifestations

00:16:39.023 --> 00:16:40.042
of the disease

00:16:40.042 --> 00:16:44.099
and so that really focuses on diagnostic
reasoning and diagnostic test and so

00:16:44.099 --> 00:16:49.042
we're gonna spend the rest of our time
today focusing on diagnostic tests

00:16:49.042 --> 00:16:52.087
so here are the learning objectives for
the rest of today by the end by the end

00:16:52.087 --> 00:16:55.068
of this lecture and honestly by the end
of your small groups tomorrow because

00:16:55.068 --> 00:16:58.082
you're gonna have to work through these
concepts in small groups it's gonna be

00:16:58.082 --> 00:17:00.031
mainly a superficial

00:17:00.031 --> 00:17:02.041
covering today of the concept

00:17:02.041 --> 00:17:05.032
and the diving into it with your simon
in small groups are really where the

00:17:05.032 --> 00:17:06.066
learnings going to happen

00:17:06.066 --> 00:17:08.999
but by the end of this series of
sessions

00:17:08.999 --> 00:17:10.006
you should be able to do some

00:17:10.006 --> 00:17:12.016
fairly basic diagnostic

00:17:12.016 --> 00:17:14.022
diagnostic question formulation

00:17:14.022 --> 00:17:17.339
you should be able to define and uh...
calculate

00:17:17.339 --> 00:17:20.959
sensitivity specificities and the
predicted values for different

00:17:20.959 --> 00:17:24.065
diagnostic test for an introduce that
concept you today and tomorrow

00:17:24.065 --> 00:17:27.048
and you should be able to explain how
risk factor

00:17:27.048 --> 00:17:30.289
that god can thrive prior probabilities

00:17:30.289 --> 00:17:33.669
and how this concept relates to
prevalence

00:17:33.669 --> 00:17:37.749
and then finally you should be able to
modify probabilities from test results

00:17:37.749 --> 00:17:39.007
through on number of different
mechanisms

00:17:39.007 --> 00:17:44.009
we introduce you to the concept obeys
probabilistic reasoning as a way of

00:17:44.009 --> 00:17:46.043
modifying probabilities over time

00:17:46.043 --> 00:17:47.059
today we're gonna use

00:17:47.059 --> 00:17:51.045
to buy two tables which is a of more
straightforward

00:17:51.045 --> 00:17:55.027
easy to conceptualize and visualize way
of modifying probabilities

00:17:55.027 --> 00:17:58.429
but you'll get more and more practice
with using that keep in mind that it is

00:17:58.429 --> 00:18:03.013
just as good as base so these are
presented to you as you should be one

00:18:03.013 --> 00:18:07.049
over the other represented the u<u>s</u>
items to put in your toolbox in portland

00:18:07.049 --> 00:18:07.057
out

00:18:07.057 --> 00:18:09.909
at different points when the need arises

00:18:09.909 --> 00:18:13.038
there also other tools that are
available that will introduce to you one

00:18:13.038 --> 00:18:14.094
called likelihood ratios

00:18:14.094 --> 00:18:16.081
and you'll get a chance to practice
these

00:18:16.081 --> 00:18:20.029
in your assignments and in your smokers

00:18:20.029 --> 00:18:24.072
so just like we had the odyssey as a
case for introducing you to use

00:18:24.072 --> 00:18:29.013
probabilistic reasoning this time really
immerse yourself in a clinical case and

00:18:29.013 --> 00:18:31.075
i want you to think about this again
just with uh...

00:18:31.075 --> 00:18:35.083
limited amount of knowledge you have
about this condition of this disease

00:18:35.083 --> 00:18:37.033
whatever you have this fall

00:18:37.033 --> 00:18:40.057
but bring to bear your experience as we
work through this case during the

00:18:40.057 --> 00:18:42.009
remaining a bit the remainder of this
like

00:18:42.009 --> 00:18:45.044
so the cases is sixty year old man

00:18:45.044 --> 00:18:47.059
who does not have heart disease

00:18:47.059 --> 00:18:50.799
who presents with sudden onset of
shortness of breath

00:18:50.799 --> 00:18:53.002
dismissed is a term that we use

00:18:53.002 --> 00:18:56.099
so here is a politically description of
the problem that you can see

00:18:56.099 --> 00:19:00.008
yesterday after he flew in from
california the day before

00:19:00.008 --> 00:19:03.091
he'll blokes suddenly in the middle of
the night at three in the morning with

00:19:03.091 --> 00:19:05.092
sudden shortness of breath

00:19:05.092 --> 00:19:08.089
so we woke up gasping for air at three
in the morning

00:19:08.089 --> 00:19:10.014
and he tells you

00:19:10.014 --> 00:19:12.057
that you ask them one question which is

00:19:12.057 --> 00:19:16.082
well was it bad when you were lying down
and that's why you setup or was it worth

00:19:16.082 --> 00:19:19.066
when you or is it about the same
regardless of whether you're setting up

00:19:19.066 --> 00:19:20.009
ur lying down

00:19:20.009 --> 00:19:24.097
because the people maybe was worse than
usual you said you know what

00:19:24.097 --> 00:19:26.007
actually is it

00:19:26.007 --> 00:19:28.082
any different online down if i'm sitting
up

00:19:28.082 --> 00:19:30.003
i'm still

00:19:30.003 --> 00:19:33.037
feeling short of breath and it won't be
up in the middle of the night

00:19:33.037 --> 00:19:36.022
all right so that is your initial chief
complaint

00:19:36.022 --> 00:19:40.023
this is something that you'll get used
to uh... as you do your data uh...

00:19:40.023 --> 00:19:43.059
queries from uh... from patients at your
data gathering

00:19:43.059 --> 00:19:44.051
from from different

00:19:44.051 --> 00:19:46.046
but you being a good clinician

00:19:46.046 --> 00:19:49.088
you start asking some follow-up
questions just like a good clinician

00:19:49.088 --> 00:19:53.022
uh... or good mccain sort of building on
the mechanic model that we introduce you

00:19:53.022 --> 00:19:54.052
to a week ago

00:19:54.052 --> 00:19:58.001
so you ask him what other symptoms were
you feeling at the time

00:19:58.001 --> 00:20:02.008
now as you get more sophisticated you
will be asking more specific questions

00:20:02.008 --> 00:20:02.085
right now

00:20:02.085 --> 00:20:05.019
sort of the about what i would expect

00:20:05.019 --> 00:20:08.025
and what seems to be able to do what
else we feeling at the time

00:20:08.025 --> 00:20:10.084
well he says does not testing

00:20:10.084 --> 00:20:15.399
he doesn't have a leg pain he doesn't
notice any swelling of his leg

00:20:15.399 --> 00:20:18.899
he says idea just come back from a long
plane ride he flew in from california

00:20:18.899 --> 00:20:21.067
solicit was about five hours

00:20:21.067 --> 00:20:23.074
nonstop

00:20:23.074 --> 00:20:27.066
and he's had no problems like this
before that he knows

00:20:27.066 --> 00:20:29.094
this shortness of breath

00:20:29.094 --> 00:20:34.001
he takes one aspirin every day and he
does a smoke a pack of cigarettes

00:20:34.001 --> 00:20:35.067
everyday

00:20:35.067 --> 00:20:38.669
so that's kind of the next phase of
diagnostic

00:20:38.669 --> 00:20:41.017
intake

00:20:41.017 --> 00:20:45.014
so the question that faces all of us
just like the mechanic faces

00:20:45.014 --> 00:20:48.007
is to be able to build a differential
diagnosis you remember me mentioning

00:20:48.007 --> 00:20:50.009
well we as clinicians

00:20:50.009 --> 00:20:52.045
still differential diagnoses all the
time

00:20:52.045 --> 00:20:55.059
and basically differential diagnosis is
a list

00:20:55.059 --> 00:20:59.929
of possibilities with associated likely
that's with associated probabilities

00:20:59.929 --> 00:21:04.047
so as we mentioned last time if you can
p of a particular condition you'd be

00:21:04.047 --> 00:21:06.006
saying that the likelihood that

00:21:06.006 --> 00:21:09.001
this particular condition is the reason
for the shortness of breath

00:21:09.001 --> 00:21:11.098
is x percent that's how you would write
that down

00:21:11.098 --> 00:21:16.169
and what you would do is you place it in
descending order of likelihood and you

00:21:16.169 --> 00:21:18.003
would be talking about wine

00:21:18.003 --> 00:21:20.059
if you could get this

00:21:20.059 --> 00:21:21.799
conceptual approach

00:21:21.799 --> 00:21:24.049
jupe all your differential diagnoses

00:21:24.049 --> 00:21:27.036
you will do well in medicine because
this is how we talk

00:21:27.036 --> 00:21:31.046
now we don't do it necessarily in such
mathematical discrete models

00:21:31.046 --> 00:21:34.076
is exactly what we talk when we talk
with another position we like you know

00:21:34.076 --> 00:21:35.013
what

00:21:35.013 --> 00:21:39.169
i think this patient has colon cancer
it's definitely more likely that he's

00:21:39.169 --> 00:21:41.037
got colon cancer than he has hemorrhoids

00:21:41.037 --> 00:21:44.049
that's kind of how we speak in barely in
formal settings

00:21:44.049 --> 00:21:45.659
when we're discussing

00:21:45.659 --> 00:21:48.074
uh... the case uh... a particular
patients case in trying to understand it

00:21:48.074 --> 00:21:49.063
yala g

00:21:49.063 --> 00:21:52.046
what we're really doing though is that
words generating a differential

00:21:52.046 --> 00:21:56.032
diagnosis and it is the regardless of
what field you're going to do

00:21:56.032 --> 00:21:58.059
you'll be doing this over and over again

00:21:58.059 --> 00:22:01.006
so you get to your first one today

00:22:01.006 --> 00:22:02.008
so now what i'd like you to do

00:22:02.008 --> 00:22:04.004
is think about

00:22:04.004 --> 00:22:08.006
what possibilities may be going on with
this particular time

00:22:08.006 --> 00:22:12.088
talk it over with your partner list two
or three things that might be going on

00:22:12.088 --> 00:22:18.023
and i will talk about what i think might
be going on

00:22:18.023 --> 00:23:17.009
e

00:23:17.009 --> 00:23:21.064
okay productive well on the five because
it's probably arctic every different

00:23:21.064 --> 00:23:22.059
about yourself

00:23:22.059 --> 00:23:24.011
at this stage that you're at

00:23:24.011 --> 00:23:25.091
but it's not wrong to try

00:23:25.091 --> 00:23:28.007
so let's just hear something you don't
have to give me a probability or

00:23:28.007 --> 00:23:29.049
anything like that

00:23:29.049 --> 00:23:38.098
just give me some possibilities of what
might be going on

00:23:38.098 --> 00:23:42.034
all materialism versus congestive heart
failure okay so we've got pulmonary

00:23:42.034 --> 00:23:43.219
embolism

00:23:43.219 --> 00:23:45.679
congestive heart failure what else do we
go

00:23:45.679 --> 00:23:50.098
sleep apnea okay great other things yeah

00:23:50.098 --> 00:23:54.026
guilty gear emphysema while you guys and
he you've gone through medical school

00:23:54.026 --> 00:23:57.074
before these are great coverage is a
great differential diagnosis absolutely

00:23:57.074 --> 00:24:01.269
ep

00:24:01.269 --> 00:24:03.087
events

00:24:03.087 --> 00:24:07.083
hotbed i'd i didn't ask him about scuba
diving and whether he had uh...

00:24:07.083 --> 00:24:10.038
at whether he had done that but
certainly that would be a follow-up

00:24:10.038 --> 00:24:12.055
question that we would act

00:24:12.055 --> 00:24:15.027
these are these are great things now
let's peace apart with these things me

00:24:15.027 --> 00:24:17.063
first of all what is a pulmonary
embolism

00:24:17.063 --> 00:24:20.017
which had pulmonary embolism you know
what it p<u>s</u>

00:24:20.017 --> 00:24:40.009
unexplained

00:24:40.009 --> 00:24:41.094
so o'clock in the long

00:24:41.094 --> 00:24:45.099
the person was sitting in mobile for a
period of time which allows rumbled sis

00:24:45.099 --> 00:24:50.029
to develop especially in the lower
extremities which can then migrate up

00:24:50.029 --> 00:24:51.088
and gets stuck in the long

00:24:51.088 --> 00:24:55.059
you stated that his shortness of breath
with sudden and so you started unpack

00:24:55.059 --> 00:24:58.027
the whole concept of rationale and my
thinking that

00:24:58.027 --> 00:25:01.023
versus some of the other things because
often times when you get a p<u>e</u> it

00:25:01.023 --> 00:25:04.087
suddenly breaks off part of your of the
clock suddenly breaks off and goes into

00:25:04.087 --> 00:25:06.022
the pulmonary basketball

00:25:06.022 --> 00:25:09.389
now you'll understate you'll start
developing the language around that but

00:25:09.389 --> 00:25:13.049
that's a great way to explain that you
also mentioned congestive heart failure

00:25:13.049 --> 00:25:15.679
now what is congestive heart

00:25:15.679 --> 00:25:18.041
art which on the spot but i was a good
differential i'm coming back into our

00:25:18.041 --> 00:25:42.015
world seven you know

00:25:42.015 --> 00:25:46.069
all right so congestive heart failure
being basically eight at in enhanced

00:25:46.069 --> 00:25:49.014
pulmonary vascular

00:25:49.014 --> 00:25:51.047
in the palm area vascular system because

00:25:51.047 --> 00:25:53.081
the heart is not able to

00:25:53.081 --> 00:25:58.051
nearly as good injection of the blood
through the periphery and so things back

00:25:58.051 --> 00:26:01.159
up for a bride of the reasons either
though

00:26:01.159 --> 00:26:04.003
orgasm pump is well it's two-step you
got valvular leakage

00:26:04.003 --> 00:26:07.095
and it backs up into the pulmonary
vasculature you increase the pressure it

00:26:07.095 --> 00:26:12.053
you cause pulmonary edema which gives
you offensive shortness of breath but as

00:26:12.053 --> 00:26:15.091
you mentioned oftentimes that'll be
accompanied by peripheral oedema because

00:26:15.091 --> 00:26:19.001
of the heart backs up from left
ventricular failure right ventricular

00:26:19.001 --> 00:26:19.083
failure

00:26:19.083 --> 00:26:20.093
than you actually have

00:26:20.093 --> 00:26:22.669
summit denying your lower extremities

00:26:22.669 --> 00:26:26.046
she doesn't according to him we haven't
done the examination you so that's the

00:26:26.046 --> 00:26:30.012
caveat here but that may be a reasonable
thing to come up with uh... to uh... to

00:26:30.012 --> 00:26:33.679
come up with in your differential and
you put it lower because there were some

00:26:33.679 --> 00:26:35.909
aspects that weren't necessarily as

00:26:35.909 --> 00:26:38.059
consistent with that bag no's' right

00:26:38.059 --> 00:26:41.033
so that's a that's a great way to
approach the differential

00:26:41.033 --> 00:26:43.001
i would mention obstructive sleep apnea

00:26:43.001 --> 00:26:43.929
overhear yet

00:26:43.929 --> 00:26:46.073
what's obstructive sleep apnea might
like that that here

00:26:46.073 --> 00:26:57.809
e

00:26:57.809 --> 00:27:00.085
pacbell now that site so what let me
just uh... unpack what you're saying

00:27:00.085 --> 00:27:01.449
there

00:27:01.449 --> 00:27:04.049
you're commenting on the fact that this
guy woke up in the middle of the night

00:27:04.049 --> 00:27:06.086
with shortness of breath now oftentimes
people who

00:27:06.086 --> 00:27:09.059
have obstructive sleep apnea don't
actually wake up

00:27:09.059 --> 00:27:12.027
but they have apnea episodes which means
that they

00:27:12.027 --> 00:27:13.429
stopped breathing

00:27:13.429 --> 00:27:17.036
for a period of time and sometimes i can
cause them to suddenly startle and wake

00:27:17.036 --> 00:27:20.005
up they don't necessarily wake up short
of breath but they can't

00:27:20.005 --> 00:27:23.065
absolutely until anyone that wakes up in
the middle of the night

00:27:23.065 --> 00:27:25.063
i'm certainly thinking about sleep apnea

00:27:25.063 --> 00:27:29.369
it's probably one of the most under
diagnosed conditions in this country

00:27:29.369 --> 00:27:32.769
i didn't know the reggie white died of
it but he certainly would be pat rescue

00:27:32.769 --> 00:27:34.839
uvic because people who have are

00:27:34.839 --> 00:27:37.048
uh... and i don't know how it will be c
was but large

00:27:37.048 --> 00:27:41.059
body habit is certainly is a risk factor
for obstructive sleep apnea

00:27:41.059 --> 00:27:45.429
also can lead to right sided congestive
heart failure so might also be connected

00:27:45.429 --> 00:27:47.065
to one of the diagnoses that we heard
early on

00:27:47.065 --> 00:27:52.005
so keep in mind that sometimes diagnoses
are completely independent of themselves

00:27:52.005 --> 00:27:55.009
revelry talked about independent
independent events

00:27:55.009 --> 00:27:58.299
sometimes different items in your
differential are actually related to

00:27:58.299 --> 00:28:02.002
other items that you differential so we
have to keep that in mind as well

00:28:02.002 --> 00:28:05.009
by legal said feel p<u>d</u> in the back and
now possible emphysema what is that

00:28:05.009 --> 00:28:07.078
and why might he be at risk for them

00:28:07.078 --> 00:28:28.659
front his

00:28:28.659 --> 00:28:29.094
baton so

00:28:29.094 --> 00:28:32.098
clearly he's got to look just to
reiterate what you're saying

00:28:32.098 --> 00:28:34.088
he's a smoker

00:28:34.088 --> 00:28:39.029
long-term smoking can cause destruction
and inflammation to the pulmonary

00:28:39.029 --> 00:28:40.008
bronchus tree

00:28:40.008 --> 00:28:42.029
andy alveolar

00:28:42.029 --> 00:28:45.026
uh... components of it what you learn
about this year and next year

00:28:45.026 --> 00:28:49.000
uh... destruction of the albee ally is
typically what we see as a mechanism

00:28:49.000 --> 00:28:50.038
towards emphysema

00:28:50.038 --> 00:28:55.049
which is one manifestation clinical
manifestation of seo p<u>d</u> and certainly

00:28:55.049 --> 00:28:56.065
can impair oxygen

00:28:56.065 --> 00:28:59.075
exchange which would make you short of
breath and destiny

00:28:59.075 --> 00:29:03.034
and maybe he's in the early stages maybe
this is just his first manifestation of

00:29:03.034 --> 00:29:03.799
that

00:29:03.799 --> 00:29:06.015
you know he said he has ended for breath
before

00:29:06.015 --> 00:29:09.033
but your focusing on his rest

00:29:09.033 --> 00:29:10.077
dot keep that in mind

00:29:10.077 --> 00:29:14.041
some people were focusing on how he
presented waking up in the middle of the

00:29:14.041 --> 00:29:15.029
night

00:29:15.029 --> 00:29:17.085
some people are focusing on risk

00:29:17.085 --> 00:29:21.004
both are absolutely critical as you get
as you generate your differential

00:29:21.004 --> 00:29:21.099
diagnosis

00:29:21.099 --> 00:29:22.075
risk

00:29:22.075 --> 00:29:27.001
drives the order often of the things in
your differential diagnosis

00:29:27.001 --> 00:29:28.559
but how u manifest

00:29:28.559 --> 00:29:31.007
also changes the order and what you're
thinking about

00:29:31.007 --> 00:29:33.035
in a different likeness

00:29:33.035 --> 00:29:35.073
both of the things that we need to walk
in with

00:29:35.073 --> 00:29:39.052
and as we think about observational
studies tying this to what doctor grover

00:29:39.052 --> 00:29:41.016
was talking about last week

00:29:41.016 --> 00:29:44.929
observation als studies give us
information about race

00:29:44.929 --> 00:29:47.027
they give us information about risk
factor

00:29:47.027 --> 00:29:50.008
that contribute to different clinical
case uh... disorders

00:29:50.008 --> 00:29:53.429
so very important to trying title of
this to get and question over here some

00:29:53.429 --> 00:29:56.072
yes

00:29:56.072 --> 00:30:00.042
back g<u>o</u>p_ d is chronic obstructive
pulmonary disease

00:30:00.042 --> 00:30:04.024
it is the long-term manifestations of
tobacco use

00:30:04.024 --> 00:30:07.057
it can manifest through either emphysema
where you have destruction of the

00:30:07.057 --> 00:30:08.083
alveolar tissue

00:30:08.083 --> 00:30:11.003
and impaired oxygen exchange as a result

00:30:11.003 --> 00:30:14.179
you can also manifest as what we call
chronic bronchitis where you have a

00:30:14.179 --> 00:30:16.000
tremendous amount of inflammation

00:30:16.000 --> 00:30:20.047
in the broncos and with mucus production
which can also cause impaired oxygen

00:30:20.047 --> 00:30:21.034
i mean

00:30:21.034 --> 00:30:22.097
uh... oxygenation

00:30:22.097 --> 00:30:25.149
so sorry i didn't identified annual

00:30:25.149 --> 00:30:28.559
learn all of these concepts as you move
on

00:30:28.559 --> 00:30:31.075
so you're doing a great job building
your first differential diagnosis now

00:30:31.075 --> 00:30:33.045
the problem is is i also said

00:30:33.045 --> 00:30:36.085
we have to start assigning probabilities
to get to these different

00:30:36.085 --> 00:30:40.013
uh... clinical manifestations of just
give you an idea of what my list was

00:30:40.013 --> 00:30:41.076
before we get started

00:30:41.076 --> 00:30:43.072
that's right

00:30:43.072 --> 00:30:45.013
congestive heart failure

00:30:45.013 --> 00:30:47.059
and that the amount exacerbate shin

00:30:47.059 --> 00:30:49.092
and i also thought about asthma which
could be another

00:30:49.092 --> 00:30:53.269
different manifestation that is not
necessarily smoking related

00:30:53.269 --> 00:30:56.749
but also uh... can contribute to airway
inflammation

00:30:56.749 --> 00:30:59.969
i didn't have obstructive sleep apnea in
my differential that doesn't mean that

00:30:59.969 --> 00:31:01.589
it's wrong to put it there

00:31:01.589 --> 00:31:05.249
um... many people would and what you'll
find is a different clinicians will

00:31:05.249 --> 00:31:09.419
bring their different behind the scenes
to their differential diagnosis

00:31:09.419 --> 00:31:12.002
of the question is what do you do when
they're all these behind seas out there

00:31:12.002 --> 00:31:17.065
and how do we assign probabilities to
the different uh... clinical

00:31:17.065 --> 00:31:19.549
uh... entities in your differential

00:31:19.549 --> 00:31:22.789
or sometimes we can do it by a gut
feeling

00:31:22.789 --> 00:31:26.098
based on what we know about the disease
based on what we know about the patient

00:31:26.098 --> 00:31:29.279
based on what we know about the for
respects

00:31:29.279 --> 00:31:32.071
and so here's my gut feeling
differential diagnosis

00:31:32.071 --> 00:31:34.096
i put p<u>e</u> at the top

00:31:34.096 --> 00:31:36.659
i could see a jeff next

00:31:36.659 --> 00:31:40.011
at thirty uh... and i put emphysema
thirteen asthma fourth

00:31:40.011 --> 00:31:43.016
and i tried to make it all add up to a
hundred percent so it was nice to meet

00:31:43.016 --> 00:31:46.539
so i could forty thirty twenty ten

00:31:46.539 --> 00:31:49.046
there is at a right answer you don't
know

00:31:49.046 --> 00:31:53.024
that's just my gut feeling but what it
does tell you is i didn't think that

00:31:53.024 --> 00:31:57.909
pete was so overwhelmingly likely and i
would put that at seventy percent and

00:31:57.909 --> 00:31:59.036
everything else down at the bottom

00:31:59.036 --> 00:32:02.006
there may be clinical conditions where
you do that but keep in mind that each

00:32:02.006 --> 00:32:04.007
one of these diagnosis

00:32:04.007 --> 00:32:05.068
had both its

00:32:05.068 --> 00:32:08.038
can uh... consistent features

00:32:08.038 --> 00:32:11.058
and something that we're just kind of
atypical

00:32:11.058 --> 00:32:14.075
why wouldn't it be a p<u>e</u> well he said
he didn't have a new leads well he'll

00:32:14.075 --> 00:32:18.007
appear on a plane ride for five hours
most people don't get a d<u>d</u>t_

00:32:18.007 --> 00:32:19.499
well maybe ever

00:32:19.499 --> 00:32:20.092
symbol that looks like

00:32:20.092 --> 00:32:23.309
y c h f not bad

00:32:23.309 --> 00:32:25.054
because there's you know there's some
things that are consistent with a but he

00:32:25.054 --> 00:32:27.045
doesn't have flirts from any of you

00:32:27.045 --> 00:32:29.075
until their fingers that will sort of
make you head

00:32:29.075 --> 00:32:31.092
and these numbers are part of making

00:32:31.092 --> 00:32:34.539
are are my manifestation of making

00:32:34.539 --> 00:32:37.669
uh... contribute communicating the head

00:32:37.669 --> 00:32:40.012
there a couple of other things you can
do with this

00:32:40.012 --> 00:32:42.007
so for example remember

00:32:42.007 --> 00:32:44.096
you can combine probabilities of
different events

00:32:44.096 --> 00:32:49.024
so what is the probability that
shortness of breath is due to be there p

00:32:49.024 --> 00:32:51.009
foresee a chap

00:32:51.009 --> 00:32:55.094
given these a particular numbers when
you guys think

00:32:55.094 --> 00:33:02.149
seventy percent

00:33:02.149 --> 00:33:05.669
if the two are mutually independent
events

00:33:05.669 --> 00:33:08.046
meaning that they're not dependent on
each other not meaning that if you happy

00:33:08.046 --> 00:33:10.659
you are not more likely to get seja

00:33:10.659 --> 00:33:11.061
or vice versa

00:33:11.061 --> 00:33:14.018
because if there is that overlap remote
from what we understand about the

00:33:14.018 --> 00:33:17.058
disease and you can't combine them by
adding so yes the answer to that would

00:33:17.058 --> 00:33:21.038
be seventy percent but remember a thing
in mind that provided that both don't

00:33:21.038 --> 00:33:22.098
happen simultaneously

00:33:22.098 --> 00:33:26.002
just as an intellectual exercise if you
thought that there might be a ten

00:33:26.002 --> 00:33:27.062
percent overlap

00:33:27.062 --> 00:33:32.088
in the likelihood that you have both p n
c h f bowing out of the same time

00:33:32.088 --> 00:33:35.012
meaning that they are dependent and then
sport

00:33:35.012 --> 00:33:36.619
that they're both likely

00:33:36.619 --> 00:33:39.389
uh... the it's possible that you're
having both of them happen at the same

00:33:39.389 --> 00:33:43.002
time then that you could combine the two
by saying what is the likelihood that

00:33:43.002 --> 00:33:45.088
you have either p or c h f

00:33:45.088 --> 00:33:47.045
but it wouldn't be seventy percent

00:33:47.045 --> 00:33:50.071
would actually be sixty percent because
there's also ten percent chance

00:33:50.071 --> 00:33:53.004
but both are happy happening
simultaneously

00:33:53.004 --> 00:33:56.059
but the good intellectual exercise to go
through again the numbers art as

00:33:56.059 --> 00:33:59.399
important as the concept that it goes
down

00:33:59.399 --> 00:34:01.005
when but to events for depend

00:34:01.005 --> 00:34:03.017
keep in mind that in medicine

00:34:03.017 --> 00:34:05.096
their are absolutely independent events

00:34:05.096 --> 00:34:08.129
and their absolutely

00:34:08.129 --> 00:34:11.909
that will be dependent and has you go
through your blocks and understand the

00:34:11.909 --> 00:34:13.789
diseases you'll get an appreciation

00:34:13.789 --> 00:34:18.799
berwyn things are determined and when
they read

00:34:18.799 --> 00:34:21.095
so basically what we're doing is worth
actually creating

00:34:21.095 --> 00:34:23.659
prior probability

00:34:23.659 --> 00:34:27.469
before we have done any further down the
track gathering with this patient

00:34:27.469 --> 00:34:29.061
re-affirm a couple of questions that we
would ask

00:34:29.061 --> 00:34:33.005
well before we do any further exit we
can do the physical exam yet

00:34:33.005 --> 00:34:36.031
we didn't do any real specific
questioning within the week testing yet

00:34:36.031 --> 00:34:37.369
we're generating

00:34:37.369 --> 00:34:41.279
it prior probability remember we did
that with the woman with the b<u>r</u>c_ a

00:34:41.279 --> 00:34:43.099
haitian that we were concerned about

00:34:43.099 --> 00:34:45.729
we had a prior probability with her
walking in

00:34:45.729 --> 00:34:47.369
do when she was twenty years old

00:34:47.369 --> 00:34:50.002
well this is a prior probability that's
based on a number of different factors

00:34:50.002 --> 00:34:52.789
that i doubt that i mentioned

00:34:52.789 --> 00:34:56.013
on the other hand you can actually
generated prior probability

00:34:56.013 --> 00:35:00.034
using some tools that are out there is
what don't want to demonstrate obscene

00:35:00.034 --> 00:35:03.669
as some of the tools that might be
helpful to you

00:35:03.669 --> 00:35:07.082
so why is there are these things called
clinical prediction rules

00:35:07.082 --> 00:35:12.009
mechanical production rules are ways of
using the literature and what we know

00:35:12.009 --> 00:35:15.026
about the literature estimate s

00:35:15.026 --> 00:35:17.659
about particular disease

00:35:17.659 --> 00:35:18.709
and

00:35:18.709 --> 00:35:23.119
the uh... the way that we did there are
a number of them that are out there

00:35:23.119 --> 00:35:26.969
pulmonary embolism is one of those
clinical diseases that actually has a

00:35:26.969 --> 00:35:29.579
number of different political
predictions and i want to sort of show

00:35:29.579 --> 00:35:30.028
you

00:35:30.028 --> 00:35:33.269
what uh... what one uh... looks like

00:35:33.269 --> 00:35:36.839
so what you have here to really think
that your slides that you can use as

00:35:36.839 --> 00:35:37.043
well

00:35:37.043 --> 00:35:39.599
this is mad calc three counts

00:35:39.599 --> 00:35:42.959
this is on the uh... you guys have
access to this and uh... they're unknown

00:35:42.959 --> 00:35:44.002
bura different uh...

00:35:44.002 --> 00:35:47.239
their number of different medical
calculators here

00:35:47.239 --> 00:35:50.092
for p what you would do is you would
enter in the day the for the particular

00:35:50.092 --> 00:35:51.889
patient

00:35:51.889 --> 00:35:57.409
and then it would give you step here in
the lower right hand corner cc

00:35:57.409 --> 00:36:00.769
so let's do that for this particular
case

00:36:00.769 --> 00:36:02.649
based on what we know right now

00:36:02.649 --> 00:36:07.579
based on what we were going out the
sixties right so we put the sixties

00:36:07.579 --> 00:36:09.013
we also know that he's made

00:36:09.013 --> 00:36:10.609
so we put that

00:36:10.609 --> 00:36:14.389
and then you'll see a whole series of
risk factors here

00:36:14.389 --> 00:36:18.819
let's say we don't deal with uh... let's
go down and see what he has

00:36:18.819 --> 00:36:22.589
we know he's got the acute onset which
means some that's another

00:36:22.589 --> 00:36:23.068
word that you learn

00:36:23.068 --> 00:36:25.579
sudden onset of this issue

00:36:25.579 --> 00:36:26.759
we click on that

00:36:26.759 --> 00:36:30.399
notice what's happening to the risk as
we go through this

00:36:30.399 --> 00:36:33.889
just being sixty years old and mail

00:36:33.889 --> 00:36:36.649
and then adding acute onset of dyspnea

00:36:36.649 --> 00:36:39.749
this risk number goes up to fifty
percent

00:36:39.749 --> 00:36:42.329
really jumps up there

00:36:42.329 --> 00:36:46.023
and if we added that he might have been
immobilized with saying this

00:36:46.023 --> 00:36:47.659
let's say he sat

00:36:47.659 --> 00:36:48.073
in a plane

00:36:48.073 --> 00:36:52.229
completely comatose for five hours
didn't move out what

00:36:52.229 --> 00:36:56.419
that would probably qualify as
immobilization

00:36:56.419 --> 00:36:58.259
let's say we clicked that

00:36:58.259 --> 00:37:02.079
you'll see that his risk of having a
p<u>e</u> with all of this

00:37:02.079 --> 00:37:04.279
is now sixty percent

00:37:04.279 --> 00:37:07.249
so my gut feeling of forty percent

00:37:07.249 --> 00:37:11.839
probably and underestimation now this is
a gut feeling this is based on

00:37:11.839 --> 00:37:15.069
spa operational stocks that are out
there and putting them into a

00:37:15.069 --> 00:37:16.509
mathematical model

00:37:16.509 --> 00:37:19.006
you can get these things for your
handheld device

00:37:19.006 --> 00:37:21.097
you can put them on the web a lot of
these are being integrated into the

00:37:21.097 --> 00:37:24.005
electronic health record for positions

00:37:24.005 --> 00:37:24.989
so that these

00:37:24.989 --> 00:37:28.189
guides can be placed right at the point
of care

00:37:28.189 --> 00:37:31.319
i'd encourage you to think about these
and try to explore some of these because

00:37:31.319 --> 00:37:34.046
they were a number of these for a number
of different conditions out there

00:37:34.046 --> 00:37:37.047
but we're gonna return to this as we go
through so right now

00:37:37.047 --> 00:37:39.096
we're starting around sixty percent

00:37:39.096 --> 00:37:42.049
as our prior probability

00:37:42.049 --> 00:37:44.094
but you realize also that there's a
number of questions here that we just

00:37:44.094 --> 00:37:48.749
don't know the answer to the right legal
fees at a fever we don't know we know

00:37:48.749 --> 00:37:51.014
that he doesn't have a history very
vascular disease

00:37:51.014 --> 00:37:54.045
we don't know if he passed out we don't
know if he's actually got one-sided

00:37:54.045 --> 00:37:55.049
lights while

00:37:55.049 --> 00:37:57.869
so there's more data we need to get

00:37:57.869 --> 00:37:59.539
so let's gather

00:37:59.539 --> 00:38:05.169
so more date

00:38:05.169 --> 00:38:08.059
so here's some more information then i'm
gonna throw at you based on this

00:38:08.059 --> 00:38:09.619
particular case

00:38:09.619 --> 00:38:13.169
you talk about family history find out
that he actually

00:38:13.169 --> 00:38:14.599
has had

00:38:14.599 --> 00:38:19.149
he has a family that is that the d<u>d</u>t_
in the past

00:38:19.149 --> 00:38:22.699
pretty for it

00:38:22.699 --> 00:38:26.063
you do a physical exam on him and you
find a his blood oxygen saturation is

00:38:26.063 --> 00:38:28.109
normal on room air

00:38:28.109 --> 00:38:30.989
so these oxygen eighty five

00:38:30.989 --> 00:38:35.359
checkers respiratory rate at sixteen
that's generally that's a little fast

00:38:35.359 --> 00:38:37.099
but it's probably okay but

00:38:37.099 --> 00:38:39.017
his pulse rate is a hundred and buy it
now

00:38:39.017 --> 00:38:43.839
united now that a hundred five ezell
elevate we would call that eka kartik

00:38:43.839 --> 00:38:45.739
so he's technopark

00:38:45.739 --> 00:38:49.005
and you examine his loans as you will
learn to do this year and you'll find

00:38:49.005 --> 00:38:52.949
when you became his patients' lungs that
he has crackles

00:38:52.949 --> 00:38:54.539
n<u>t</u>s<u>b</u>'s

00:38:54.539 --> 00:38:56.339
user crackles are sort of

00:38:56.339 --> 00:38:57.053
they sound like crackers

00:38:57.053 --> 00:38:59.489
we've ever listen to rice crispy

00:38:59.489 --> 00:39:02.859
that's what it sounds like a bit sounds
with inspiration you would get crap that

00:39:02.859 --> 00:39:06.429
usually indicates that there's some
degree of a team up in the long some

00:39:06.429 --> 00:39:10.007
degree of swelling in the long and as
the albee a liar trying to expand

00:39:10.007 --> 00:39:12.949
they pop open up a very easy way but
enough

00:39:12.949 --> 00:39:15.089
tough way because there's a lot of
surface tension at each of you

00:39:15.089 --> 00:39:19.119
level because of the fluid in the
interstitial space

00:39:19.119 --> 00:39:23.649
he's also got leases leases are
indications of airway obstruction small

00:39:23.649 --> 00:39:26.189
airways obstruction in the long

00:39:26.189 --> 00:39:29.095
but you'll also notice he doesn't have a
problem which means that he doesn't have

00:39:29.095 --> 00:39:33.339
this sort of uh... inflammation in the
pleural space which will learn about

00:39:33.339 --> 00:39:36.015
and he doesn't have evidence of
consolidation consolidation would give

00:39:36.015 --> 00:39:39.039
you some clues that he might have an emo

00:39:39.039 --> 00:39:41.589
we don't have either of those

00:39:41.589 --> 00:39:44.449
but you also examine is like and you
find that even though he didn't think it

00:39:44.449 --> 00:39:47.569
was a swollen it absolutely is well

00:39:47.569 --> 00:39:49.869
and you feel of any

00:39:49.869 --> 00:39:50.081
below his knee

00:39:50.081 --> 00:39:54.002
most of the time we should be able to
feel the danes attorney but if they're

00:39:54.002 --> 00:39:56.013
inflamed possibly because of a clock

00:39:56.013 --> 00:39:58.439
you might feel below the knee

00:39:58.439 --> 00:40:01.929
you get a chest x-ray that's normal

00:40:01.929 --> 00:40:05.088
and you get the cagey in its shows that
his heart's going fast but nothing's

00:40:05.088 --> 00:40:08.269
besides that

00:40:08.269 --> 00:40:10.869
so now what we do is we go back

00:40:10.869 --> 00:40:14.489
to the clinical prediction

00:40:14.489 --> 00:40:17.094
calculator and cd about entering in this
data

00:40:17.094 --> 00:40:22.169
so the additional data that will get

00:40:22.169 --> 00:40:23.089
he not only is uh...

00:40:23.089 --> 00:40:27.023
sixty years old and mailing it to keep
this thing out and let's say he's

00:40:27.023 --> 00:40:29.169
immobilized he was a mobile as

00:40:29.169 --> 00:40:34.999
we now find that he's gotten lateral
excellent

00:40:34.999 --> 00:40:37.609
but that he also has leases

00:40:37.609 --> 00:40:40.609
contracts

00:40:40.609 --> 00:40:44.489
no notice what happens to pay attention
to the number as i enter the zip

00:40:44.489 --> 00:40:48.038
i started out with sixty percent by
aditi lateral leg swelling what we're

00:40:48.038 --> 00:40:50.589
getting really close for x seventy five
percent

00:40:50.589 --> 00:40:52.719
but this person's that p

00:40:52.719 --> 00:40:53.095
upholding a bit

00:40:53.095 --> 00:40:57.059
remember we're talking about as long as
even though

00:40:57.059 --> 00:40:58.499
the race

00:40:58.499 --> 00:40:59.529
his lead

00:40:59.529 --> 00:41:02.009
because if you've got to cut your leg
you're more likely to throw that but we

00:41:02.009 --> 00:41:05.026
have a pulmonary embolism those two are
not

00:41:05.026 --> 00:41:06.619
independent features

00:41:06.619 --> 00:41:08.769
those who are dependent effects

00:41:08.769 --> 00:41:12.269
so it dries it up to seven six percent
but knows what happened when i clicked

00:41:12.269 --> 00:41:14.469
on visas and practice

00:41:14.469 --> 00:41:18.269
that number within seventy five percent
of the thirty five percent

00:41:18.269 --> 00:41:19.919
so what in your mind

00:41:19.919 --> 00:41:21.839
must you be thinking

00:41:21.839 --> 00:41:24.099
the presents of crackles and we use is
actually make

00:41:24.099 --> 00:41:28.219
pulmonary embolism last like

00:41:28.219 --> 00:41:32.559
in fact pulmonary embolism the number
one clinical finding in the long for p

00:41:32.559 --> 00:41:33.729
is nothing

00:41:33.729 --> 00:41:36.409
subtotal e normal pulmonary exam

00:41:36.409 --> 00:41:38.889
just because you have a normal palm
trees and doesn't mean you don't have a

00:41:38.889 --> 00:41:40.239
disease

00:41:40.239 --> 00:41:42.066
as an important consideration but keep
in mind that this is a way of

00:41:42.066 --> 00:41:43.058
quantifying

00:41:43.058 --> 00:41:44.709
how much

00:41:44.709 --> 00:41:49.013
dropped there is so we ever did all this
data and we're now at around thirty five

00:41:49.013 --> 00:41:50.449
percent

00:41:50.449 --> 00:41:52.319
so turns out i was about

00:41:52.319 --> 00:42:06.169
or a percent was pretty close to thirty
five pst

00:42:06.169 --> 00:42:10.047
there are interactional terms that are
built into the mathematical model here

00:42:10.047 --> 00:42:13.579
so if you look above the rest

00:42:13.579 --> 00:42:18.159
and sold those interactions are built
into how he calculates the factor some

00:42:18.159 --> 00:42:20.809
which then translates to what the risks

00:42:20.809 --> 00:42:23.093
so yes there are interaction terms
between these things

00:42:23.093 --> 00:42:26.629
and it's calc it's all done in the
background

00:42:26.629 --> 00:42:28.799
clinician you know i'm not gonna do that

00:42:28.799 --> 00:42:31.669
and i'm certainly not to be able to look
at a study be able to know how to do

00:42:31.669 --> 00:42:34.329
that that's why these calculators to be
very helpful

00:42:34.329 --> 00:42:37.109
it'll give you an idea are we weigh off

00:42:37.109 --> 00:42:39.719
or are we about right is this guy is

00:42:39.719 --> 00:42:42.096
was my initial gut feeling over on
target yeah

00:42:42.096 --> 00:42:45.839
was kind of on target even when we did
more data gathering

00:42:45.839 --> 00:42:47.016
but you also get a sense

00:42:47.016 --> 00:42:50.066
uh... why how different features
increase and decrease the likelihood

00:42:50.066 --> 00:42:59.649
which is a good learning tool

00:42:59.649 --> 00:43:02.689
rate

00:43:02.689 --> 00:43:05.119
so the question is of why is

00:43:05.119 --> 00:43:06.919
smoking and wake nodding here

00:43:06.919 --> 00:43:10.529
the answer is is that smoking and wait
for actually not considered risk factors

00:43:10.529 --> 00:43:12.679
for p

00:43:12.679 --> 00:43:15.769
when they've looked at these studies
what you might think of boy there smoker

00:43:15.769 --> 00:43:17.299
they're more likely to have a clock

00:43:17.299 --> 00:43:19.059
into israel

00:43:19.059 --> 00:43:21.269
just because you're a smoker doesn't
mean that you're more likely to have a

00:43:21.269 --> 00:43:22.309
p<u>e</u>

00:43:22.309 --> 00:43:25.039
now certain smokers do carry increase
from body chris

00:43:25.039 --> 00:43:28.069
if you're a young woman who smoking on
or contraceptives

00:43:28.069 --> 00:43:32.629
you already higher risk of developing a
lower extremity d<u>d</u>t_

00:43:32.629 --> 00:43:33.819
at is clear

00:43:33.819 --> 00:43:36.829
but that's not necessarily what we're
talking about here

00:43:36.829 --> 00:43:39.879
over the lot big picture it doesn't
contribute risk

00:43:39.879 --> 00:43:42.709
it also could be because the studies
were done but in this case is because

00:43:42.709 --> 00:43:51.659
they're not respect

00:43:51.659 --> 00:43:52.509
uh...

00:43:52.509 --> 00:43:55.839
so here's the question if you are
thinking that there is a nother

00:43:55.839 --> 00:43:59.599
possibility on your differential
diagnosis that is either equally or more

00:43:59.599 --> 00:44:04.019
likely does it drive this down the
absentee answers absolutely it does

00:44:04.019 --> 00:44:06.043
and there are limits to these clinical
prediction

00:44:06.043 --> 00:44:09.052
so this is done in a vacuum their other
clinical prediction rules

00:44:09.052 --> 00:44:13.031
where you can actually have a button
that says is an alternative diagnosis

00:44:13.031 --> 00:44:17.549
equally or more likely when you do that
people drop your s

00:44:17.549 --> 00:44:20.044
because it knows that there may be other
things going up this prediction will

00:44:20.044 --> 00:44:25.029
didn't do that

00:44:25.029 --> 00:44:29.045
station had a family history of a d<u>d</u>t_
but not a personal history dvd if you're

00:44:29.045 --> 00:44:33.009
interested in what that would have done
you could do it if he had a dvd in the

00:44:33.009 --> 00:44:34.269
past

00:44:34.269 --> 00:44:38.539
it drives up from thirty five to fifty

00:44:38.539 --> 00:44:41.979
yet family history of some of his family
with d

00:44:41.979 --> 00:44:45.289
all these are great questions but the
most important thing to keep in mind is

00:44:45.289 --> 00:44:48.299
you don't just have to go on gut feel

00:44:48.299 --> 00:44:51.289
at these clinical prediction rules for
common diseases which are the ones that

00:44:51.289 --> 00:44:51.097
are out there

00:44:51.097 --> 00:44:53.074
can help you understand

00:44:53.074 --> 00:44:58.249
the clinical manifestations of a
particular disease

00:44:58.249 --> 00:45:00.859
so what does this have to do with what
we do

00:45:00.859 --> 00:45:05.129
well keep in mind we're now

00:45:05.129 --> 00:45:06.589
we are now at

00:45:06.589 --> 00:45:09.089
um having completed our data gathering
things were based

00:45:09.089 --> 00:45:12.058
with the prior probability of about
thirty five percent

00:45:12.058 --> 00:45:14.949
at the station is happy

00:45:14.949 --> 00:45:16.009
and so what we need to do you think
about

00:45:16.009 --> 00:45:18.819
do we need to get a test

00:45:18.819 --> 00:45:21.289
because the question that should be
going through your mind is the thirty

00:45:21.289 --> 00:45:25.379
five percent high enough at allstate
yahoo dot abt and got a pulmonary

00:45:25.379 --> 00:45:26.016
embolism

00:45:26.016 --> 00:45:28.089
we're gonna treat you as such

00:45:28.089 --> 00:45:31.149
hopefully thirty five percent is too low
for even you

00:45:31.149 --> 00:45:34.529
to say boy i don't think that i would
point to treat based on that certainly

00:45:34.529 --> 00:45:39.499
would be low for most of the nation's we
need to probably get some sort of text

00:45:39.499 --> 00:45:44.489
so what this is a how those bridges over
into diagnostic test

00:45:44.489 --> 00:45:47.489
so here is the question what we do with
this number

00:45:47.489 --> 00:45:51.249
well if there was a test that existed
that could rule in pulmonary embolism as

00:45:51.249 --> 00:45:52.022
the diagnosis

00:45:52.022 --> 00:45:54.008
with a hundred percent sense certainty

00:45:54.008 --> 00:46:00.529
we would be saying that probability of
this of a patient having a p

00:46:00.529 --> 00:46:01.021
due to the

00:46:01.021 --> 00:46:02.074
at the test is positive

00:46:02.074 --> 00:46:05.619
is a hundred percent

00:46:05.619 --> 00:46:09.269
and the question i would ask you is what
is the stressful

00:46:09.269 --> 00:46:13.239
what we call this test the boot stain

00:46:13.239 --> 00:46:18.289
the gold standard generally exist for
more most conditions where they're is

00:46:18.289 --> 00:46:22.099
where works for the past week after the
finding of the best will stand at the

00:46:22.099 --> 00:46:23.249
top

00:46:23.249 --> 00:46:25.013
uh... it may not be the best test

00:46:25.013 --> 00:46:26.036
that we can envision

00:46:26.036 --> 00:46:27.069
but it's the best test

00:46:27.069 --> 00:46:32.229
that is available

00:46:32.229 --> 00:46:35.499
and the question that i would ask is if
you use the gold standard tests and you

00:46:35.499 --> 00:46:37.859
found it

00:46:37.859 --> 00:46:39.002
the test was positive

00:46:39.002 --> 00:46:42.095
is the probability of an alternative
diagnosis remember that a test test

00:46:42.095 --> 00:46:46.339
that's a gold standard is only the gold
standard or particular diagnosis

00:46:46.339 --> 00:46:48.509
let's say there's another diagnosis

00:46:48.509 --> 00:46:49.719
that you're interested in

00:46:49.719 --> 00:46:50.869
is it zero

00:46:50.869 --> 00:46:52.028
if the test is positive

00:46:52.028 --> 00:46:53.043
the answer is no

00:46:53.043 --> 00:46:54.279
because

00:46:54.279 --> 00:46:56.043
sometimes you have two things going on

00:46:56.043 --> 00:46:58.249
sometimes there are vents

00:46:58.249 --> 00:47:00.999
that are related to each other dependent
on each other

00:47:00.999 --> 00:47:02.071
for sometimes you just have bad luck

00:47:02.071 --> 00:47:03.639
as a patient

00:47:03.639 --> 00:47:06.619
and you have both pulmonary embolism and
c<u>h</u>a_

00:47:06.619 --> 00:47:08.089
but the most important to keep thing to
keep in mind

00:47:08.089 --> 00:47:12.279
is that we are always looking to see
what the gold standard is

00:47:12.279 --> 00:47:16.459
but we can't always used to go see

00:47:16.459 --> 00:47:19.789
so what is that not stick testing people
but not the testing

00:47:19.789 --> 00:47:23.043
the the goal of diagnostic testing is to
help us modify probabilities

00:47:23.043 --> 00:47:24.008
we talked about how

00:47:24.008 --> 00:47:29.021
we modify probabilities based on history
taking physical exam other simple tests

00:47:29.021 --> 00:47:32.015
complex s like the ones we're gonna talk
about

00:47:32.015 --> 00:47:34.629
will help modify probabilities as well

00:47:34.629 --> 00:47:36.129
but they cost a lot of money

00:47:36.129 --> 00:47:39.016
and so we need to approach argues a
diagnostic tests

00:47:39.016 --> 00:47:42.269
judicious

00:47:42.269 --> 00:47:45.069
so in order to understand what we're
looking for work in a study about

00:47:45.069 --> 00:47:48.119
diagnostic test we need to understand

00:47:48.119 --> 00:47:53.999
how people related items to test

00:47:53.999 --> 00:47:56.049
really does relate instead of

00:47:56.049 --> 00:47:57.549
the patient

00:47:57.549 --> 00:47:59.092
uh... population were interested in

00:47:59.092 --> 00:48:02.049
what we're really trying to use the
following

00:48:02.049 --> 00:48:05.169
a disease state

00:48:05.169 --> 00:48:07.799
what is the disease that we're trying to
diagnose

00:48:07.799 --> 00:48:11.109
in this particular case if ur interested
in another test to use

00:48:11.109 --> 00:48:14.389
it would be the disease state would be a
pulmonary embolism

00:48:14.389 --> 00:48:15.579
intervention

00:48:15.579 --> 00:48:19.809
would actually be the test itself so
what tester we interested in his room

00:48:19.809 --> 00:48:22.279
looking through the literature

00:48:22.279 --> 00:48:25.999
the comparison group is not another
therapy but it was in the therapeutic

00:48:25.999 --> 00:48:26.077
questions

00:48:26.077 --> 00:48:28.749
it's the gold standard

00:48:28.749 --> 00:48:30.049
so you're trying to compare

00:48:30.049 --> 00:48:32.099
a test of interest

00:48:32.099 --> 00:48:34.839
against what is the best test that's out
there

00:48:34.839 --> 00:48:37.459
the problem with the best test that's
out there is that it's frequently

00:48:37.459 --> 00:48:38.032
infeasible

00:48:38.032 --> 00:48:41.032
sometimes dangerous even though it's the
best s so we're looking for an

00:48:41.032 --> 00:48:44.054
alternative test that we can use i can
help us with our page so that those

00:48:44.054 --> 00:48:46.279
favoritism

00:48:46.279 --> 00:48:49.879
and then the outcome of interest that
were interested in is the performance of

00:48:49.879 --> 00:48:51.149
the text

00:48:51.149 --> 00:48:53.879
that's the fundamental

00:48:53.879 --> 00:48:55.359
and you will be able to

00:48:55.359 --> 00:48:56.018
do this

00:48:56.018 --> 00:48:59.035
over and over again as you're looking at
different studies and we've this is part

00:48:59.035 --> 00:49:00.289
of the assignment

00:49:00.289 --> 00:49:02.139
for two more

00:49:02.139 --> 00:49:04.459
so let's practice

00:49:04.459 --> 00:49:07.689
as we've seen the sixty location without
heart disease is presenting with some

00:49:07.689 --> 00:49:09.199
nonsense shortness of breath

00:49:09.199 --> 00:49:11.229
we're considering a p

00:49:11.229 --> 00:49:14.489
that would be our disease or our p

00:49:14.489 --> 00:49:19.269
protest and ask us to consider is a test
collabera profusion scheme

00:49:19.269 --> 00:49:21.024
cowbell asian perfusion scan

00:49:21.024 --> 00:49:23.939
is something that's been around for a
long time

00:49:23.939 --> 00:49:25.589
it basically

00:49:25.589 --> 00:49:28.027
in the test a patient in hale's

00:49:28.027 --> 00:49:31.899
or radio nuclei partner

00:49:31.899 --> 00:49:36.629
and we see where that radio nuclei
particle goals

00:49:36.629 --> 00:49:40.239
and in addition the patient gets
injected with that same radio nuclear

00:49:40.239 --> 00:49:41.139
particle

00:49:41.139 --> 00:49:43.959
and we see based on the blood flow

00:49:43.959 --> 00:49:45.249
that particle goes

00:49:45.249 --> 00:49:46.769
we take pictures

00:49:46.769 --> 00:49:49.849
simplistic explanation but i thought you
really need to know at this point

00:49:49.849 --> 00:49:51.849
and what we're looking for is

00:49:51.849 --> 00:49:54.029
where does the air go

00:49:54.029 --> 00:49:56.549
that blood doesn't go

00:49:56.549 --> 00:49:59.489
but that there's a place where the air
goes that the blood doesn't go that

00:49:59.489 --> 00:50:02.669
would likely be where o'clock would be

00:50:02.669 --> 00:50:04.399
api

00:50:04.399 --> 00:50:07.599
but that's what happens is that the
clock obstructs blood flow to that

00:50:07.599 --> 00:50:10.219
particular place

00:50:10.219 --> 00:50:12.549
now the gold standard

00:50:12.549 --> 00:50:16.489
four diagnosis of a pulmonary embolism
something we call pulmonary and

00:50:16.489 --> 00:50:17.379
geography

00:50:17.379 --> 00:50:20.739
which is where you were actually
injecting died and watching where the

00:50:20.739 --> 00:50:22.089
blood blow goes

00:50:22.089 --> 00:50:24.069
you see a picture of a b q scan on the
top there

00:50:24.069 --> 00:50:28.939
on the bottom is a very grainy picture
of a pulmonary angiogram

00:50:28.939 --> 00:50:31.409
just keep in mind that an angiogram

00:50:31.409 --> 00:50:33.509
more costly

00:50:33.509 --> 00:50:37.379
slightly more dangerous

00:50:37.379 --> 00:50:38.949
the gold standard

00:50:38.949 --> 00:50:42.539
but we wouldn't because it's costly and
more dangerous we wouldn't offered to

00:50:42.539 --> 00:50:43.819
all patients

00:50:43.819 --> 00:50:44.819
because if we did that

00:50:44.819 --> 00:50:48.027
the risk that we would in anyone who we
suspect has a p

00:50:48.027 --> 00:50:51.013
the amount of complications and cost
that we would entail

00:50:51.013 --> 00:50:53.009
would be mass

00:50:53.009 --> 00:50:56.011
that's what we're looking to see is is
of the few scan which is actually

00:50:56.011 --> 00:50:58.609
fairly

00:50:58.609 --> 00:51:00.539
really fairly

00:51:00.539 --> 00:51:02.349
at not terribly dangerous

00:51:02.349 --> 00:51:05.039
whether that would be good enough
compared to the gold standard for many

00:51:05.039 --> 00:51:07.009
of the geography

00:51:07.009 --> 00:51:10.229
what were interested in is diagnostic
performance

00:51:10.229 --> 00:51:16.709
so that is the pico recognize the test

00:51:16.709 --> 00:51:20.499
but before thinking about it became
scandal then elation perfusion scamper

00:51:20.499 --> 00:51:23.099
first question we have to ask

00:51:23.099 --> 00:51:26.299
kena beat you scan actually even be used

00:51:26.299 --> 00:51:28.779
now you will be asking this question as
a clinician

00:51:28.779 --> 00:51:31.039
but before you can even go to market

00:51:31.039 --> 00:51:32.033
as a possible test

00:51:32.033 --> 00:51:35.041
there's some fundamental questions about
a diagnostic test

00:51:35.041 --> 00:51:38.599
that require some definitions that you
should be aware

00:51:38.599 --> 00:51:42.299
and they thought this on to concerts
accuracy and precision in order for a

00:51:42.299 --> 00:51:43.084
test to be used

00:51:43.084 --> 00:51:47.579
in the literature and study for possible
use it needs to be accurate

00:51:47.579 --> 00:51:50.399
and it needs to be precise or whining
about it

00:51:50.399 --> 00:51:53.054
what accuracy means at the results of
the test

00:51:53.054 --> 00:51:57.209
corresponds consistently with from
result

00:51:57.209 --> 00:52:00.839
not going to result in terms of
diagnosing the disease

00:52:00.839 --> 00:52:02.519
but the correct about

00:52:02.519 --> 00:52:05.619
meaning that it'd be q skin if i object

00:52:05.619 --> 00:52:08.709
the radio nuclei and i say it goes to
the long

00:52:08.709 --> 00:52:10.959
if you go to the law

00:52:10.959 --> 00:52:15.029
and if i inhale the radio nuclei and i
say he should be inhaled into the

00:52:15.029 --> 00:52:16.569
alveolar space

00:52:16.569 --> 00:52:21.039
it should actually be inhaled into the
alveolar sticks

00:52:21.039 --> 00:52:21.729
fundamental

00:52:21.729 --> 00:52:25.219
but keep in mind that there is a clone
of work that happens

00:52:25.219 --> 00:52:28.619
prior to attest going to study

00:52:28.619 --> 00:52:31.229
that requires this to happen

00:52:31.229 --> 00:52:33.839
and there's a lot of science behind us

00:52:33.839 --> 00:52:35.071
so needs to be accurate enemies

00:52:35.071 --> 00:52:39.056
besides we're learning about the size
twelve decision means that if you do

00:52:39.056 --> 00:52:43.309
with over and over again on the same
patient you'll get the same result

00:52:43.309 --> 00:52:45.479
with a reliable test

00:52:45.479 --> 00:52:50.229
the repeated values on the same sample
resume results in the same down

00:52:50.229 --> 00:52:53.529
so in the same patient you do it once
you do it again five minutes later you

00:52:53.529 --> 00:52:54.066
you five minutes later

00:52:54.066 --> 00:52:56.739
missing uh... results actually happened

00:52:56.739 --> 00:52:58.929
that's the preciseness

00:52:58.929 --> 00:53:00.489
you need to have both

00:53:00.489 --> 00:53:02.739
they're actually three different

00:53:02.739 --> 00:53:04.609
possibilities that tend to happen

00:53:04.609 --> 00:53:05.909
when early

00:53:05.909 --> 00:53:09.109
phase studies are done and diagnostic
tests

00:53:09.109 --> 00:53:10.051
the first is the one that you want

00:53:10.051 --> 00:53:13.041
want to be highly accurate and highly
precise pointed out that you're good to

00:53:13.041 --> 00:53:13.091
go

00:53:13.091 --> 00:53:16.839
ready to go to step two and study its
characteristics

00:53:16.839 --> 00:53:17.989
however

00:53:17.989 --> 00:53:20.359
you can have something very precise

00:53:20.359 --> 00:53:22.699
but be completely inaccurate

00:53:22.699 --> 00:53:25.709
that's what's represented conceptually
by the bulls on where you have a lot of

00:53:25.709 --> 00:53:28.017
different numbers there clustering all
around the same area

00:53:28.017 --> 00:53:31.989
but it's actually not doing what you
think it's doing

00:53:31.989 --> 00:53:34.149
and then there is sometimes when you
have

00:53:34.149 --> 00:53:37.589
reasonable accuracy it's all clustered
around the bulls eye

00:53:37.589 --> 00:53:38.929
but low precision

00:53:38.929 --> 00:53:40.529
their hat you get different

00:53:40.529 --> 00:53:42.839
answers each time you do it

00:53:42.839 --> 00:53:45.039
so what do you do in these different
situations

00:53:45.039 --> 00:53:48.459
well the first into a single one step to
your butt

00:53:48.459 --> 00:53:51.249
the second one you gotta think about
calibration

00:53:51.249 --> 00:53:56.609
and you need to reset or maybe you need
to relook at the reagents veteran vault

00:53:56.609 --> 00:53:59.179
at a particular test itself

00:53:59.179 --> 00:54:02.629
in the last one unfortunately you gotta
start over

00:54:02.629 --> 00:54:06.279
if you've got a bunch of if you're a
test is not precise how usable could

00:54:06.279 --> 00:54:07.559
actually be

00:54:07.559 --> 00:54:10.029
you have to actually get the precision
death

00:54:10.029 --> 00:54:12.067
again this may seem fundamental in
foundational

00:54:12.067 --> 00:54:16.489
but there are so many things that don't
make it to market for even testing

00:54:16.489 --> 00:54:18.449
because they don't meet these criteria

00:54:18.449 --> 00:54:21.529
important for you to keep him

00:54:21.529 --> 00:54:25.749
once you make it past that first phase
then you can decide

00:54:25.749 --> 00:54:30.439
diagnostic performance it what the
diagnostic performances the o of the

00:54:30.439 --> 00:54:32.969
pico for diagnostic tests

00:54:32.969 --> 00:54:34.022
and so fundamentally

00:54:34.022 --> 00:54:37.079
i would ask you to think about two
things

00:54:37.079 --> 00:54:41.059
any good diagnostic study does this

00:54:41.059 --> 00:54:43.769
they take a well-defined group of people

00:54:43.769 --> 00:54:46.679
who are at risk for a particular
condition

00:54:46.679 --> 00:54:49.099
a whole population of them and they
expose them to

00:54:49.099 --> 00:54:52.159
the experimental tests

00:54:52.159 --> 00:54:54.969
and the gold st

00:54:54.969 --> 00:54:57.699
everyone in the study needs to have both

00:54:57.699 --> 00:55:01.139
and if you compare the test results

00:55:01.139 --> 00:55:02.379
experimental tests

00:55:02.379 --> 00:55:04.679
and the gold standard

00:55:04.679 --> 00:55:07.879
keep in mind you don't want that patient
population to be

00:55:07.879 --> 00:55:11.089
everyone having the disease a hunter
percent of them having the disease

00:55:11.089 --> 00:55:12.051
you need to have a fair number

00:55:12.051 --> 00:55:15.003
of people who don't have the disease in
order to test

00:55:15.003 --> 00:55:16.959
the test characteristics

00:55:16.959 --> 00:55:20.079
well that's the fundamental premise of
any good diagnostic study and you'll be

00:55:20.079 --> 00:55:22.629
able to recognize he's

00:55:22.629 --> 00:55:26.439
what we can do is determine the strength
of the association

00:55:26.439 --> 00:55:30.459
between the study results of the
diagnostic test

00:55:30.459 --> 00:55:34.119
of interest and the gold standard
missiles he just comparing the two how

00:55:34.119 --> 00:55:36.289
well do they compare against each other

00:55:36.289 --> 00:55:39.679
the strength of all of that statistical
significance is the degree of

00:55:39.679 --> 00:55:44.659
correlation begin the accuracy or not
yet received the test results all the

00:55:44.659 --> 00:55:49.329
two different tests that are on in this
particular set

00:55:49.329 --> 00:55:52.829
clinical significance is another factor
we're not going to talk about that

00:55:52.829 --> 00:55:54.209
right now

00:55:54.209 --> 00:55:58.719
well what we need to do is focus on
statistical significance

00:55:58.719 --> 00:56:01.639
so before we break i'm just going to

00:56:01.639 --> 00:56:04.689
present to you with the way that i'm
gonna ask you

00:56:04.689 --> 00:56:05.799
to think about

00:56:05.799 --> 00:56:07.091
and represent that data

00:56:07.091 --> 00:56:11.049
from a diagnostic study that does
exactly what

00:56:11.049 --> 00:56:13.979
what i'd just out

00:56:13.979 --> 00:56:17.079
a diagnostic study you are looking at

00:56:17.079 --> 00:56:18.349
the

00:56:18.349 --> 00:56:21.579
performance of the test of interest

00:56:21.579 --> 00:56:23.076
and the gold standard he's y

00:56:23.076 --> 00:56:26.019
t

00:56:26.019 --> 00:56:28.259
better out there to buy two table

00:56:28.259 --> 00:56:30.119
to be able to represent

00:56:30.119 --> 00:56:34.469
how those the study participants a sort
themselves based on how the test of

00:56:34.469 --> 00:56:35.339
interested

00:56:35.339 --> 00:56:37.909
and how the gold standard label

00:56:37.909 --> 00:56:40.869
across the top you always

00:56:40.869 --> 00:56:44.129
you always uh... the columns are
represented by those that tested

00:56:44.129 --> 00:56:45.006
positive

00:56:45.006 --> 00:56:48.024
for the disease based on the gold
standard medical center

00:56:48.024 --> 00:56:50.023
work theoretically calling a
hundred-percent

00:56:50.023 --> 00:56:54.679
therefore each identified those in the
population who have the disease

00:56:54.679 --> 00:56:57.019
and those that test negative by the gold
standard

00:56:57.019 --> 00:57:00.409
will be in the second call

00:57:00.409 --> 00:57:02.419
but all of these populations

00:57:02.419 --> 00:57:03.077
in the study

00:57:03.077 --> 00:57:07.046
there will be some of those that also
tested positive based on the

00:57:07.046 --> 00:57:11.739
experimental test you're interested

00:57:11.739 --> 00:57:14.619
and some that test lead

00:57:14.619 --> 00:57:16.092
and sometimes they're going to agree

00:57:16.092 --> 00:57:18.699
with what the gold standard says

00:57:18.699 --> 00:57:22.269
such as inbox a and boxy

00:57:22.269 --> 00:57:24.019
sometimes they're going to disagree

00:57:24.019 --> 00:57:25.999
with what the gold standard set

00:57:25.999 --> 00:57:29.239
based on box b and boxy

00:57:29.239 --> 00:57:32.024
for simplicity safe keep in mind that we
arent we are

00:57:32.024 --> 00:57:36.459
assuming that the gold standard is a
hundred percent

00:57:36.459 --> 00:57:39.044
so we're just gonna assume that whatever
the gold standard said is true

00:57:39.044 --> 00:57:42.899
and we're comparing it against test of
interest

00:57:42.899 --> 00:57:46.069
each of these boxes have different names
that are going to come get introduced to

00:57:46.069 --> 00:57:47.079
you

00:57:47.079 --> 00:57:48.589
does that work

00:57:48.589 --> 00:57:53.729
disease are are labeled correctly by
experimental tasks

00:57:53.729 --> 00:58:00.199
as having the disease based on the gold
standard are called true positives

00:58:00.199 --> 00:58:01.859
their inbox it

00:58:01.859 --> 00:58:05.339
those that are correctly labelled as not
having the disease by the experimental

00:58:05.339 --> 00:58:12.699
test relative to the gold standard are
considered true naked

00:58:12.699 --> 00:58:13.089
those that are

00:58:13.089 --> 00:58:17.069
falsely labeled as having the ditsy

00:58:17.069 --> 00:58:18.299
based on the tax

00:58:18.299 --> 00:58:21.719
but they actually build because the gold
standard sent me one

00:58:21.719 --> 00:58:26.559
are called false positives

00:58:26.559 --> 00:58:30.689
and those that are falsely labeled at
not having the disease

00:58:30.689 --> 00:58:32.349
when they actually do

00:58:32.349 --> 00:58:34.679
are called false names

00:58:34.679 --> 00:58:36.769
the standard nomenclature

00:58:36.769 --> 00:58:38.009
gotta remember it

00:58:38.009 --> 00:58:40.061
fairly straightforward false positives
false names

00:58:40.061 --> 00:58:44.199
these areas of agreement these are the
areas of disagreement

00:58:44.199 --> 00:58:46.049
what we're going to do no

00:58:46.049 --> 00:58:47.009
is picked up

00:58:47.009 --> 00:58:49.009
with our

00:58:49.009 --> 00:58:52.069
figuring out how we use this to define
test characteristics

00:58:52.069 --> 00:58:55.229
so let's take a five minute break

00:58:55.229 --> 00:58:57.359
and then we will come back and talk
about

00:58:57.359 --> 99:59:59.999
the test characteristics better rise
from this to my teeth