What's the difference between accuracy and precision? - Matt Anticole
-
0:07 - 0:11As the story goes,
the legendary marksman William Tell -
0:11 - 0:15was forced into a cruel challenge
by a corrupt lord. -
0:15 - 0:18William's son was to be executed
-
0:18 - 0:22unless William could shoot
an apple off his head. -
0:22 - 0:27William succeeded, but let's imagine
two variations on the tale. -
0:27 - 0:29In the first variation,
-
0:29 - 0:33the lord hires a bandit to steal
William's trusty crossbow, -
0:33 - 0:37so he is forced to borrow
an inferior one from a peasant. -
0:37 - 0:41However, the borrowed crossbow
isn't adjusted perfectly, -
0:41 - 0:43and William finds that his practice shots
-
0:43 - 0:48cluster in a tight spread
beneath the bullseye. -
0:48 - 0:53Fortunately, he has time
to correct for it before its too late. -
0:53 - 0:54Variation two:
-
0:54 - 0:59William begins to doubt his skills
in the long hours before the challenge -
0:59 - 1:02and his hand develops a tremor.
-
1:02 - 1:05His practice shots still cluster
around the apple -
1:05 - 1:07but in a random pattern.
-
1:07 - 1:09Occasionally, he hits the apple,
-
1:09 - 1:13but with the wobble,
there is no guarantee of a bullseye. -
1:13 - 1:15He must settle his nervous hand
-
1:15 - 1:19and restore the certainty in his aim
to save his son. -
1:19 - 1:24At the heart of these variations
are two terms often used interchangeably: -
1:24 - 1:26accuracy and precision.
-
1:26 - 1:28The distinction between the two
-
1:28 - 1:32is actually critical
for many scientific endeavours. -
1:32 - 1:36Accuracy involves how close you come
to the correct result. -
1:36 - 1:40Your accuracy improves with tools
that are calibrated correctly -
1:40 - 1:42and that you're well trained on.
-
1:42 - 1:44Precision, on the other hand,
-
1:44 - 1:48is how consistently you can get
that result using the same method. -
1:48 - 1:52Your precision improves
with more finely incremented tools -
1:52 - 1:55that require less estimation.
-
1:55 - 1:59The story of the stolen crossbow
was one of precision without accuracy. -
1:59 - 2:03William got the same wrong result
each time he fired. -
2:03 - 2:08The variation with the shaky hand
was one of accuracy without precision. -
2:08 - 2:11William's bolts clustered
around the correct result, -
2:11 - 2:15but without certainty of a bullseye
for any given shot. -
2:15 - 2:18You can probably get away
with low accuracy -
2:18 - 2:21or low precision in everyday tasks.
-
2:21 - 2:25But engineers and researchers
often require accuracy -
2:25 - 2:30on microscopic levels with
a high certainty of being right everytime. -
2:30 - 2:33Factories and labs increase precision
-
2:33 - 2:36through better equipment
and more detailed procedures. -
2:36 - 2:39These improvements can be expensive,
so managers must decide -
2:39 - 2:44what the acceptable uncertainty
for each project is. -
2:44 - 2:46However, investments in precision
-
2:46 - 2:49can take us beyond
what was previously possible, -
2:49 - 2:52even as far as Mars.
-
2:52 - 2:55It may surprise you that NASA
does not know exactly where -
2:55 - 2:59their probes are going to touch down
on another planet. -
2:59 - 3:02Predicting where they will land
requires extensive calculations -
3:02 - 3:06fed by measurements
that don't always have a precise answer. -
3:06 - 3:11How does the Martian atmosphere's density
change at different elevations? -
3:11 - 3:14What angle will the probe
hit the atmosphere at? -
3:14 - 3:17What will be the speed
of the probe upon entry? -
3:17 - 3:21Computer simulators run thousands
of different landing scenarios, -
3:21 - 3:24mixing and matching values
for all of the variables. -
3:24 - 3:26Weighing all the possibilities,
-
3:26 - 3:29the computer spits out
the potential area of impact -
3:29 - 3:33in the form of a landing ellipse.
-
3:33 - 3:38In 1976, the landing ellipse
for the Mars Viking Lander -
3:38 - 3:44was 62 x 174 miles,
nearly the area of New Jersey. -
3:44 - 3:46With such a limitation,
-
3:46 - 3:51NASA had to ignore many interesting
but risky landing areas. -
3:51 - 3:54Since then, new information
about the Martian atmosphere, -
3:54 - 3:56improved spacecraft technology,
-
3:56 - 4:02and more powerful computer simulations
have drastically reduced uncertainty. -
4:02 - 4:06In 2012, the landing ellipse
for the Curiosity Lander -
4:06 - 4:10was only 4 miles wide by 12 miles long,
-
4:10 - 4:14an area more than 200 times
smaller than Viking's. -
4:14 - 4:18This allowed NASA to target
a specific spot in Gale Crater, -
4:18 - 4:23a previously un-landable area
of high scientific interest. -
4:23 - 4:26While we ultimately strive for accuracy,
-
4:26 - 4:30precision reflects our certainty
of reliably achieving it. -
4:30 - 4:33With these two principles in mind,
-
4:33 - 4:34we can shoot for the stars
-
4:34 - 4:37and be confident
of hitting them every time.
- Title:
- What's the difference between accuracy and precision? - Matt Anticole
- Speaker:
- Matt Anticole
- Description:
-
View full lesson: http://ed.ted.com/lessons/what-s-the-difference-between-accuracy-and-precision-matt-anticole
When we measure things, most people are only worried about how accurate, or how close to the actual value, they are. Looking at the process of measurement more carefully, you will see that there is another important consideration: precision. Matt Anticole explains what exactly precision is and how can help us to measure things better.
Lesson by Matt Anticole, animation by Anton Bogaty.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 04:53
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