Day 022 - 12 Sep 94 - Page 46
1 that kind of very long history, if you are going to try to
2 identify when they started and why they started?
3 A. I think almost certainly most cancers have a long, as
4 we say, gestation period.
5
6 Q. It is not like a virus that you either get in a week or
7 you do not?
8 A. No. You have introduced viruses. I mean, virus
9 infections may be a responsible factor in the development
10 of some cancers.
11
12 Q. That was not quite the point I was making. All I mean is
13 cancer is always going to be some kind of long process?
14 A. Usually, I think that is right, yes.
15
16 Q. So really for people doing cohort studies, there is a
17 great responsibility on them to do it over a substantial
18 period of time for it to have any significant evidential
19 result?
20 A. Of course, this is one of the criticisms of case
21 controlled studies is that, you know, when you start
22 looking at the controls, you take a healthy group of
23 people who do not have the illness, you are comparing
24 people with the illness, right? You have actually
25 identified a population who have, say, breast cancer; you
26 then select out a group of people who do not have breast
27 cancer and see what happens to them, OK?
28
29 Q. An equivalent population?
30 A. Yes, and because they are healthy, you know, again it
31 may be some time, you have this health delay factor (as it
32 is called) where people, you know, you might see a lower
33 incidence of breast cancer in the group that you have
34 selected because they are actually healthy at the time you
35 start to study them. So, this can give misconceptions
36 about cancer incidence in this new group that you have
37 started to look at compared with the group you have taken
38 who have got the disease and, therefore, are a group from
39 the past.
40
41 Q. Yes. Is another area of problems with cohort studies, and
42 probably case controlled studies as well, the accuracy of
43 actually recording people's diets or people recording
44 their own diet even probably more of a problem?
45 A. I think with all of these epidemiological studies, be
46 they prospective or retrospective, one of the major
47 difficulties is identifying diet. This is, when we talk
48 about methodology, most of the authors in all of the
49 publications state that this has been a real problem for
50 them is to identify it because, you know, they talk about
51 average portion size. Now, what does an "average portion"
52 mean, and things like that. There has been real
53 difficulty in identifying the actual diet that people
54 eat. People's recall of diet is very poor. I mean, I am
55 not sure that I, without a great deal of effort,
56 can remember what I ate a month ago, for example.
57
58 Q. Yes. I cannot remember if I ate anything at all!
59
60 MR. JUSTICE BELL: I was going to say, if you were asked what
