[Dorothy Bishop] I'm going to talk today about evaluating alternative intervention approaches to dyslexia. [slide with talk title] The conventional approaches that you get really tend to rely on the fact that we've now got of evidence that most children with dyslexia have problems in what is called phonological awareness, that is, they don't necessarily hear all the different sounds in speech, and therefore have difficulty relating them to letters when they are trying to read. And most of the interventions that are mainstream these days would focus on trying to train children to identify sounds in words and relate them to letters. But this sort of intervention has been shown to be effective, and there have been a number of large scale studies. But nevertheless, it has to be fairly prolonged for some children, and there are children for whom, even though they can learn this way to actually sound out words and read, they don't necessarily read fluently. It's still an effort for them, and they don't sort of get to the degree of automaticity that you might expect, And it's certainly the case that methods that work for many children don't work for all children, and there is a hard core of children who remain very hard to treat. It is for this reason that many parents do get very concerned about whether there is something else they should be doing if they are finding that their child is either not getting intervention, or that the intervention doesn't seem to be working very well. And there are a whole load of things out there that are on offer, and the problem for the parents, I think - and/or indeed for adults who themselves, might want to have further intervention for dyslexia - is that they want to know, "how do I distinguish something that might work for me", from something that is just some sort of snake-oil merchant who is out there to make money. And that's what I want to try and address today. principally from the perspective of how you might evaluate scientific evidence that people put forward. But perhaps before going onto that, it's worth going into some relatively commonsense things. I would say that there are certain things that should ring alarm bells if people are advertising some sort of treatment for child dyslexia. The first thing is if the intervention has been developped by somebody who has no academic track record, no experience of doing research in this field, and hasn't published anything in this field, if the intervention isn't endorsed by people in the mainstream dyslexia field, that should also sound a note of caution. Of course, the mainstream people aren't always right. It's possible that somebody with no background will develop something marvelous. But if that were the case, you would expect it to be pretty quickly picked up by people in the mainstream, who are really, on the whole, pretty keen to find things that will work. And you obviously want to look at whether somebody is asking for a lot of money for something that hasn't been proven. And what is also, to my mind, a worrying sign, is if somebody promoting a treatment is relying heavily just on testimonials from individuals who claimed to have been cured, rather than having any sort of proper scientific evaluation or kind of controls. And it's worth noting that human beings have a tendency to be terribly impressed by testimonials, and even myself, as somebody with a scientific training, I find if, you know, I've got headaches and somebody comes along and says: "I was cured by such and such, and I went to my herbalist and it worked", you know, you're often very tempted to be much more swayed by that sort of evidence than by a pagefull of numbers and figures. And this just a human tendency: we are naturally built to really take advice from other people and to rely on what they tell us. But in the contexts of these sorts of interventions, that's really quite dangerous, because, when somebody gives a testimonial, that's just one person, their only individual experience, And people you don't hear from tend to be the people who tried it, and it didn't work. And you don't know how many of them there are: there may be thousands of them. But they're not going to publicize the fact that they tried it and it didn't work. And so, testimonials are often very much at odds with more scientific evaluations. .... to turn out that when somebody says there is scientific evidence for what they're doing, how you should interpret that. And that's jolly difficult even for scientists sometimes: there is disagreement - let alone for the general public. But again, I think, there are some sort of general rules of thumb that you can go by for telling that a treatment is likely to be effective. And when I discuss this, I'm going to illustrate it by taking the example of the Dore treatment - that's DORE, named after Wynford Dore, it's originator. ANd I'm picking on this largely because it is a non-mainstream treatment that isn't widely accepted by the experts, and yet it does claim that there is some scientific evidence to support it, which has lead the scientists to look at it quite critically and quite carefully, which is what we would do with any scientific evidence that comes along: once it's out in the public domain and published, people tend to go and look at it as carefully as they possibly can. Now, the Dore method is interesting to us, because it does illustrate the case where there is disagreement as to whether the evidence is showing that its' effective or not. And so, what I want to explain is why it is the case that despite this published evidence, most of the experts are not impressed of the efficacy of the Dore treatment. But the general points that I'll make would apply to any other treatment that was out there, whether (?) there was evidence being produced. So, first of all, what is the Dore method? Well, it's a method that has been proposed for curing problems that are thought to originate in the part of the brain called the cerebellum, which is at the back of the brain, and it was developed by Wynford Dore as a method for helping his dyslexic daughter. He has written a book about the history of how this came to became (?) about, and he was a classic instance of a parent who was rather desperate to help his daughter who, for many years, had been through the educational system and failed, and was getting increasingly depressed. And he tried various things, he talked to various experts, and he ended up with this program that's been put forward, which is an individualized program, where the child follows various sorts of exercises, which are done for about ten minutes twice a day, over quite a long period of time, varying, depending on the severity of the problem, from maybe 6 months to 2 years. And the child is assessed at regular intervals and different exercises may be prescribed. Now, the theory behind the Dore method is that dyslexia and other learning difficulties - it's not just dyslexia it claims to help, but also Attention Deficit problems ...(?) hyperactive - are thought to arise within the cerebellum: the cerebellum just doesn't develop normally, and the argument is that you can have different cerebellar impediments in different people, and that's why you can get this range of different symptoms, but that you can diagnose them by specific tests of test of mental and physical coordinations. And what you are then supposed to do is these exercises, which are not anywhere fully described in the public domain, because they are commercially sensitive, but there are some examples given, and it's clear that what they do is focused largely on training balance and hand-eye coordination in children. So you might be asked to stand on a cushion on one leg, or to throw a bean bag from one hand to another while you are doing that, just stand on a wobble board (?) and balance, or to follow something with your eyes in a particular way. So, the idea is that these are all things that the cerebellum is involved in, by training up the cerebellum, you may improve its general abilities. So, what is the evidence for this underlying theory? Well, it's not a proven theory, but there is some support for it. Certainly, people trying to look at what is going on in the brain in dyslexia have proposed many different theories about what the underlying causes might be. If you look at the brain in a brain scanner of somebody with dyslexia, it typically looks totally normal. There's certainly no big holes in the head or anything like that, that you are going to see on a scanner. But the argument is being made that there may be regions of the cerebellum that are perhaps slightly smaller than they should be or not functioning quite as they should be. And this theory has some support, although not everybody would agree with it and there is certainly other theories equally plausible at the moment that are around. The notion - the cerebellum is important for getting things automated. So you can - when you learn to drive a car, first of all, it's very slow and effortfull, and you have to think about everything you do. By the time you are a skilled driver, it's no longe the case that you have to do that, you just drive around without thinking about it. You can do all sorts of other things while you are driving. So, the argument is that with reading, most people, similarly, become very automatic in how they learn to read: you do it without thinking about it, but for the dylexic it remains effortfull because the cerebellum is not functioning normally and it's the cerebellum that helps you get your skills automatized. And in support of this, it has been argued that in many people with dyslexia, there are some associated problems with motor coordination, ..... (?) physical skills and so on, and that too could be a sign of a problem with the cerebellum. Again, that's fairly controversial, it's not being found in all children, and the arguments go to and fro. But this is not a sort of theory that is particularly disapproved of by the mainstream. People are debating it. The difficult stumbling block, though, for the Dore approach to treatment comes with the idea that if you train the motor skills, that is a sort of coordination between different muscles and movements and between their eyes and hands, that this will somehow have a knock-on effect on things like reading. And indeed, David Randall and colleagues, who published this initial study on the treatment, describe it as something of a leap of faith, because the cerebellum is actually known to be a very complicated organ, with lots of different regions, which are fairly independent from one another. So there is no real reason to suppose that if you train one part of the cerebellum, it will have somehow a generalized benefit. And indeed, you could say: "Well, if it were the case that this is true, if you'd had a chance, you would go to skateboarding, or playing ping-pong, or things like that, ....... (?) or perhaps ballet dancing, things that require balance and coordination, that should protect you against dyslexia". There is really not much evidence for that, on the contrary, there is some very good sportsmen who - gymnasts and people with dyslexia. So it is hard to see how the logic of saying "Train these motor skills and somehow the whole cerebellum function some day improves2 But what does the published evidence look like? Because the theory might be, you know, questionable, but basically, what the parents are going to say is, "What matter is, does it work?" Well, there is a published study on the intervention, which claims that it shows that it really does work if you compare children who have the intervention and children who don't. And two papers have been reported - one from the initial phase of the study, and the other from a subsequent phase - And they are reported in the Journal of Dyslexia which, in 2003, published the first paper which was on just under - started with a sample statistics on the 300 children who were all attending a .... (?) primary school. And the researchers went in and screened all the children on the dyslexia screening test, to pull out children who would be suitable for enrolment in the study. But the first thing that is more important to note is that these were not children who had a very high rate of diagnosis of dyslexia. So, there were 35 in the group, and about a third of those came out as having a strong risk of dyslexia on this dyslexia screening test. Another 21% came out with a mild risk, but about half of these children were not really ...... (?) in this category and they were just picked because their schools (?) were relatively lower compared to the other children. And there were only a total of 6 children who had previously been diagnosed with dyslexia, out of the 35. There were a couple with a diagnosis of dyspraxia and one with ADHD diagnosis. So this is not really a sample consisting of children really with severe problems on the whole. There were few in there with major difficulties. Nevertheless, the originators of the treatment would argue even quite mild problems might be worth treating with this and so you could argue this study is nevertheless of value. So what they did, they started out well in this study: they divided the children randomly in treated and untreated groups, which is, as I am going on to explain later, is an important part of a good study. And if you look at the results that are described on the promotion materials of the DORE organization, they are all in Dore's book that he published, "Dyslexia, the miracle cure", he described the results as stunning and said that reading age increased threefold, comprehension age increased almost fivefold and writing skills by what he described as "an extraordinary 17-fold". Of course, everybody reading that think "Wow, my child is going to take off like a rocket if we put him on this intervention." But unfortunately, these figures are really a classic instance of how statistics can be manipulated in a very misleading way. So, for a start, they were not based on any comparison between the control children and the untreated children - sorry, the control children and the treated children. They were - instead, they just took all the children who would be treated and looked at how they did on a group reading test that had been administered by the school every year. And the children had had this on two occasions prior to the intervention - so, 3 months before it started and a year before that - and on two occasions after the intervention, after this whole long 4-year period. And what the researchers did was to really just plot the average schools of the group over these 4 time periods and show that if you compared the amount of change from the first time point to the second, which was before they had had any treatment, it was a certain amount and if you then compared the second to the third time point, so the treatment had been going on (?) between those two, there was a different amount of change. And then they divided one by the other and showed that there was this threefold improvement. But it's a very, very misleading way of depicting these data, because if you look at them on a graph, here, you can see that the only odd thing about the data - well, there's two odd things about the data: one is that at most time points, these children are reading at absolutely normal levels. So it's not clear why they are regarded as having risk for dyslexia; and the one time point when they're not, is the time point 3 months before they are involved in the study, where there is a bit of a drop. But it's really not an impressive demonstration of change and this division of one time period by another is very misleading, because it just gives double weighting to this one low period of three months before the treatment started. And they did the same thing again with these other figures of massive increases that they talk about, using data from the SATS tests administered by teachers, which are not really regarded as particularly precise or rigorous tests, and really group children in a fairly global way at level 2, 3 or 4. Level 2 is average for 7 year old, 3 is average for 9 year old, and 4 is average for an 11 year old. And to give you an idea of the sort of misleading nature of these massive changes they talk about, on the writing test, where there is this incredible change that they talk about, of a 17-fold increase, the score at age 8, the average score was 2.5, which is about what you'd expect from a 8 year old. At age 9, it was 2.56, which is a little bit better, but not much. And then, they argue, the intervention came in, and at age 10, the children scored 2.95. They are still rather below where they ought to be at the age of 10. It looks as if on this particular writing assessment, the children were just rather creeping along. But because the difference between 2.53 and 2.56 is less than the difference between 2.56 and 2.95, they make a big computation of dividing one by the other, actually coming out with the number 17, which is a wrong number (?): it's actually 13. So there is a 13-fold change. But if you look at the overall numbers, this is really not so an impressive game at all. It's really a very misleading way of presenting the numbers. So, most people would say, this is really smoke in mirrors in terms of using statistics in a way that isn't really valid. The other thing that is of notice is that all these results that have given so much publicity in promoting the treatment about these massive changes, haven't talked about the control group at all. They've just talked about, "Well, we've got these children, before treatment they did this, and after treatment they did that, and it has all gone up". And of course, if schools do go up after treatment, it's not necessarily because the treatment works: There are lots of other reasons you need to bear in mind. And the first of which is just, on some things, you get better because you get older, so that if you were to measure shoe sizes before the DORE treatment and after it, it would go up, but it wouldn't mean that it made your feet grow bigger. Now, clearly, that's a silly example in most cases, because people try to use measures that don't necessarily change with age, or that are adjusted in some way for age. But it's important to bear that in mind when people are talking about changes on things like - the DORE program, they talk about changes on balance, balance improves dramatically after the program. These are measures that have not been adjusted for age at all, and so, some of these changes could well be due to the fact that the children are getting older and getting better at doing these things because of that. Another uninteresting reason why schools may improve is that the children may be having some other sort of special help. So, if a child is having reading difficulty, they may very well be getting some special help at the school, in addition to following this program. And that may be what's causing the change, rather than the particular intervention you are interested in. What's very well known, of course, is the placebo effect, which is a sort of concept coming from medicine, which also says that you can get better just because you think you are going to get better, because you think somebody has done something effective. And in the case of educational treatments, you can see effects where - because the teachers and the parents and the children themselves are all full of expectations of how this is going to improve them - there is more motivation: everybody gets positive attention and this itself can cause positive effects. The fourth reason, which is often neglected, because it really doesn't affect things in medicine so much, but in education, it's actually rather important, using the sort of thing like reading tests: you can have practice effects. So you can get better upon some things, just because you've done it before. And we've seen this quite a lot with language tests, for example, that we give to children, where, the first time you test a child, they don't know what to expect, they don't know what's coming, you aske them to do something that's unfamiliar and they are a little bit nervous, maybe. You test them again on the same thing a month later: they are much, much better, simply because they've done it before and they are calmer about it, they know what to expect, and so on. So you can get practice effects that can make quite a difference, just because you know what to expect and you are familiar with the whole situation of the test. The fifth reason - and the last one, you'll be pleased to hear - why people may improve for no good reason is the hardest to explain and it's something known as regression to the mean, and it's just a statistical artefact, which has to do with, if you pick somebody because they're bad at something, the odds are, when you test them on a second occasion, they'll be a little bit better (?). The converse is also true: if you pick somebody who is very good, they tend to get a little bit worse when you test them a second time. Why should that be? The reason why this occurs is because our measures are not entirely perfect an accurate - I'm showing a graph here, where we have a measure that is almost perfect, and you test people on two occasions, and you just will see that their scores on time 1 and time 2 are identical: we are assuming that there is no genune change. If you do that, then you don't get regression to the mean, because the measure is perfect and if you test them a second time, they'll get exactly the same sort of score. And what you can see on the right hand side of the graph here, is people divided up according to the average score they started with. So we've put people into groups who were very poor to start with, who were medium, less good and so on. And these are just fictitious data made up to illustrate the point. So you just generate these numbers by saying, "We've got a measure that has this particular characteristic that if you measure on one occasion, on another occasion it remains pretty much the same". So then, you don't get regression to mean and you get people to maintain their position across time. So if you then see change, you can say "Well, it's genuine change." But most of our measures are not like that, most of our measures are not perfectly correlated: that means, you measure them on one time, and another time, and they actually change because of all sorts of things. Things like the particular test items that you're using, whether you are in a good mood, whether you've made a lucky guess in some items. And what you can see is that if you do that, that some people's scores go up with time, some people's go down with time. But on average, if you start with a low score, the odds are, you come a little bit closer to the average when you are tested on another occasion. If you start with a high score, you get a little bit worse. And this is nothing to do with genuine change: it's just to do with the fact that our measures are imperfect. And it has been argued that this is a major reason - all sorts of treatments that work (?) but don't really work. It's just that it looks as if you've seen a change, and you tend to attribute it to the treatment. Now, this sounded very depressing, because it means there's all sorts of reasons why we can see change, and how do we distinguish whether we've got a genuine change due to our treatment? But the fact is that you can control for most of these things if you do a study that has a control group. That's why those who are trying to do scientific evaluations are really keen to include control groups in studies and argue that they are essential. Because if you have another group of children who have been selected to be as similar as possible to your treated group, and are the same tests before and after the period where the treated group are treated, you are actually controlling for the effects of maturation, the effects of any other intervention they might be having, practice effects in particular, and also this dreadful regression to the mean. All of those things can be then taken into account. And in so far as they have effects, what you would expect to see is that you may see improvement in your control group because of these spurious things that we don't really want to see. And then you can say, "well there is more improvement in the treated group" (?) and it is that difference that is really critical. It doesn't actually control to use - if you have a group who have not been given any treatment - it doesn't control for placebo effects. So you've still got the problem that maybe your treated group will improve just because everybody is focusing on them with great excitement. But you could actually also have control for that, and it's becoming increasingly popular in this field to say that what you should have is a control group who are actually given some alternative treatment. So, for example, if you are interested in a treatment that might improve reading, you could either get children some standard educational treatment that they are getting anyway So if your claim is that you are doing better than a phonological-based treatment, you could have a control group given that treatment and see if you are making really that much difference, or you might prefer to say, "Well, let's treat something else, let's give children training in something completely different that isn't focused on reading, but nevertheless could benefit them in other ways." And then you can do that sort of comparison. So what about the DORE study, because I mentioned at the outset, when talking about this study, that they did have a control group. But so far, talking about the results, are only mentioned (?) the dramatic changes that they saw, which ignored the control group. The interesting thing is that when you look at their control group, it illustrates perfectly the importance of having a control group. So, on they dylexia risk's score, where a high score is bad, they had a change in the treated group, from 0.74 to 0.34. So you think: "Wow, that's great, these children's risks for dyslexia have really come down." In the control group, the average score changed from 0.72 to 0.44. Now, you could say: "Well, it's not so big a change." The trouble is, with groups this size, you can't really tell whether that's meaningful. But certainly, what is clear is that both groups improved on the dyslexia screening test, even though the control group had not had the intervention. So, it really illustrates the point very clearly that on a lot of these measures, everybody gets better, even if they are not treated. Now, if we look at the more precise data that they presented, they presented average scores on the different subtests from the dyslexia screening tests, I won't talk about all of them, I have got a fuller presentation where I do talk about all the different measures they use and I don't want to sort of be accused of delberately hiding things, but I think the tests that people would be most interested in are the literacy tests. So, you undertake the DORE treatment because you want to get better at reading and writing, if you are a parent of a dyslexic child, at any rate. So, looking at the results on those tests, what they found was that there were a total of 4 tests that had to do with literacy directly. And on one of those, it looked as if the treated group did better than the untreated group. But there is a problem with that, though, because on this reading test, the untreated - the control group are actually right on the average score for their age at the start of the treatment - at the start of the study. So, in a sense, you could argue, "Is there really room for improvement ...... (?) school absolutely average, whereas it just so happened that the children who had treatment started a little bit lower and therefore had more improvement. And their improvement was not dramatic, one has to say as well. Their school went up from 3 to 3.5, on a scale of 0 to 10. On the other measures, again it illustrated that on two of them, everybody improved, regardless of whether they had the treatment. And on the third one, nobody changed very much at all. So, this is not dramatic evidence of improvement but you could argue: "Well, nevertheless there was one measure that looked a little bit promising." But they then, in the second phase of the study, went on to give the control group the same treatment, and they published this in 2007. So we now don't anymore have a control group as everybody has been treated: one group early on, and the other group with a delayed time scale. And they presented the data between time 1 at the start of the study and right at the end of the study, when everybody had had this treatment. But when you look at the results there, it's clear that there really is a, you know, no persistent improvement in reading. In fact, the mean scores for the children having the delayed treatment on the reading test have now really gone down, rather than up, at the end of treatment. And the general impression, I would say, is that there is nothing very stunning going on here, certainly nothing that matches the description that you get on the promotion materials for the intervention. So, overall, I would argue that the evidence for gains associated with this treatment is really not at all compelling. First of all, the claims that are made for stunning changes are all coming from analyses where they didn't incorporate the controls and they just tried to argue that any change you see at the time must be due to the treatment. and not taking into account all these other factors. And on reading measures, where there was control group data available, there was an initial small gain in the treated group, but it wasn't sustained by the end of the study. So, it really doesn't look terribly promising. Now, this is why in general, I think it's true to say this: I don't know of anybody in the dyslexic community who is an advocate - in the academic community who is an advocate of the DORE treatment, other than people that are directly associated with the DORE organization. And so, the reason really is just that the evidence is not at all compelling, although the study was small and you could argue a larger study should be done. There is a real mismatch between the claims that are being made and the evidence that is available. But the interesting thing is also why so many people seem to nevertheless regard this as an effective treatment. If the testimonials are to be believed, there are many satisfied customers and happy parents who feel that their children have been helped. I think there is quite an interesting set of reasons why this may be so. And one is that there is a well known - in the psychological field - well known human tendency to think that something that you've put in a lot of time and money too, was worthwhile. It's called cognitive dissonance, and it means that if you've actually put in the effort, you tend to feel that there was an effect. You have to somehow resolve this sort of inconsistency, otherwise, in your mind. And this was beautifully illustrated, not by the trial of the DORE treatment, but in another trial, which was a very nicely well-conducted trial of something called Sunflower therapy, which is a rather holistic approach to intervention for dyslexia that involves kinesiology and physical manipulation, massage, homeopathy, herbal remedies and neurolingusitc programming. And there was a very rigorous study done for this, and what was interesting about it was that, like so many of these things, they didn't really find a lot of evidence for any better change in the clinical versus the control group, although, to some extent, both groups were securing (?) their schools were improving. What they did find, though, is that the children themselves had higher self-esteem if they had undergone the Sunflower treatment, but that also, 57% of the parents did think that Sunflower therapy was effective in treating their child. So there is a clear mismatch between what the study showed of the objective evidence on the children's learning difficulties, and what the parents actually thought. It is possible that this could be related to the fact that the children's scores did improve, but if you didn't know that the control children had also improved, you might attribute that to the therapy - but also to the fact that people were again being given a lot of encouragement, there was a lot invested in that treatment, and then there might well (?) have been some sort of sense of cognitive dissonance there. There's also a strong human tendency to be impressed by certain kinds of explanation that get more biological about dyslexia, particularly those such as the DORE treatment that get more neurological and claim to be doing something to the brain in treating dyslexia. There was a beautiful study done - published - in 2008, not on dyslexia, but just more generally on people's tendency to be impressed by scientific eyplanations. and what these researchers did was to give people explanations of psychological phenomena that are well known and they either gave them a good explanation or they gave them a not very good explanation that was more like just a re-description of the effect, and asked people to judge whether this was a good explanation or not. And what was fascinating about this study was that in general, people were quite good at doing this: even if they had no familiarity or background in psychology, they could distinguish a good explanation from a bad one. But what they found was that if they added some verbiage that just talked about the brain in various ways, and said, "This result came about because brain scans showed it", or "because we looked at the frontal lobes", people were much more impressed with the bad explanations. So a good explanation didn't get any better when you added all this neuroscience waffle, but if you added neuroscience waffle to a bad explanation, people thought it not so bad. And so, there is a tendency to be very impressed by anything that talks about, adds the brain in to an ........ (?) explanation. And I think this is used by people who then try and add spurious neuroscience sometimes to their accounts of their particular promissing theory. And it really is not - we shouldn't allow ourselves to be mislead. So I think, to sum up, there are a number of barriers to objective evaluation of intelligence, which, to some extent, functions about (?) our human condition, that we are not naturally good at taking in lots of numbers and looking at graphs and trying to sort of take into account alternative explanations. We tend to be impressed when we hear other people tell us that something has worked and it's hard - you have to almost guard yourself against the tendency to do that and to look rather for the hard evidence, to look for the actual numerical data. We have to be very careful when people start giving us explanations that have got a lot of neuroscience in them and check out, is this real neuroscience or is it just put in there to impress us? We have to be aware of the effect of cognitive dissonance and the tendency to believe some things simply because we have invested time and money in it and, most importantly, we have to bear in mind that there will be effects on children's performance of maturation, of our expectations, of just get practising on things, and there are also these dreadful statistical artefacts that can make it look as if a change has occurred, when it's really not particularly impressive. But I think, if one bears these things in mind, the bottom line is really: "Look for evidence from studies that have got adequate controls" and if you do, you'll be in - a standard, I think, by how far you can see improvements in children, even if they haven't had the treatment. and there are lots of things that will make things a lot better, just with the passage of time. But if you really want to demonstrate that there has been an effective treatment, you do have to show an improvement relative to a control group, rather than just, somebody started out not so good and is now a little bit better after the treatment. I hope that that might give you some useful indicators when trying to look at new treatments that are out there and on offer, and for a more detailed account of some of this work, there are various - there is a powerpoint presentation with notes on my website on this topic.