Day 252 - 20 May 96 - Page 24
1 number of people to study. What is, then, the minimum that
2 you consider to be a satisfactory number?
3 A. Well, nowadays, if one is thinking are carrying out an
4 investigation on human subjects one has to look at the
5 variable that you are measuring, which would be blood
6 cholesterol. You have to look at the standard deviation
7 within the population, which is a measure of the
8 variability and statisticians then work out how many people
9 you would need to use in the study to achieve the level of
10 significance what was acceptable. This is a rather
11 complicated procedure which I usually get somebody else to
12 do for me, but they will end up by saying you will need 103
13 people in your study, minimum, or 22, depending on how
14 variable the factors that you are measuring. Obviously, the
15 greater variability in the population the larger number of
16 people you will have to use to demonstrate a difference.
17
18 Q. Because one of your studies that was disclosed was on ten
19 people was it not?
20 A. Yes.
21
22 Q. But you would regard that as satisfactory?
23 A. Yes, indeed. I think, if I could explain that, we
24 were not comparing these ten people with another ten
25 people. We were looking at these ten people. Making
26 measurements on them, and doing something to them and
27 making more measurements. Rather like the one with 20
28 subjects in it that you saw here, but ten people was more
29 than adequate to demonstrate what we were doing in that
30 particular piece of work.
31
32 Q. The one with 5 people, that was not comparing them with
33 other people, was it? That was just within the 5?
34 A. Yes, yes, it was looking at their response to being
35 given something.
36
37 Q. So, that would fall in the same category as your own
38 research?
39 A. If you are looking specifically at that paper, we were
40 comparing two breakfasts, one very high in fat and one
41 virtually fat free. In doing a study like this what would
42 have made this a better study -- if I am looking at the
43 right one -- yes, is -- no, the number was really too
44 small. Ideally, if you are carrying out two different
45 procedures on a group of people what you do is split the
46 group and carry out both procedures simultaneously and then
47 at the end of your measurements you swop them over and
48 those that have been on a high fat diet would go on low fat
49 diet and those that had been on the low fat diet would go
50 on the high fat diet. This is called crossover study. The
51 advantage of doing that is that you can take account of
52 factors which could influence your results. For example,
53 if you are doing a study on soups and you were you given a
54 high fat diet and made measurements, and then after that
55 give them a low fat diet, it could be that the low fat diet
56 coincides with when they are sitting examinations or when
57 environmental temperature has gone up by ten degrees, and
58 that could influence their behaviour and it could influence
59 the result.
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