Day 022 - 12 Sep 94 - Page 51
1 3 and tab 5, because they reach opposing conclusions, do
2 they not?
3
4 MR. MORRIS: One is about breast cancer.
5 A. And one is about colon cancer.
6
7 MR. MORRIS: And one is about colon cancer. I am going to come
8 on to that, if I may.
9
10 MR. JUSTICE BELL: There are slightly more women in the -----
11 A. This was a study of women.
12
13 Q. Yes, but there were slightly more in the breast cancer
14 than the colon cancer one?
15 A. I think it is probably just that the follow-up period
16 of time was longer.
17
18 Q. About 700 or so.
19
20 MR. MORRIS: Can I just continue with the results from the
21 abstract. It concludes: "No association was found for
22 vegetable fat. The relative risk of colon cancer in women
23 who ate beef, pork or lamb as a main dish every dish every
24 day, was 2.49 at a 95 per cent confidence interval, 1.24
25 to 5.03, as compared with those reporting consumption less
26 than once a month". Is that a very high finding?
27 A. You can see that the confidence limits are very wide;
28 they go from 1.24 to 5.03. Basically what that means is
29 that there might be a 24 per cent increased risk or there
30 might be a fivefold increased risk. You know, they have
31 averaged it out. The average is two-and-a-half fold risk.
32
33 Q. I see.
34 A. But one worries about confidence intervals being so
35 wide.
36
37 Q. Is this a problem with cohort studies, though?
38 A. No, it does not only apply to cohort studies. If
39 anything, it is more likely to occur with case-controlled
40 studies where you get very wide confidence limits. The
41 wider the confidence limits that you see, the more one is
42 concerned about, you know, the validity of the results.
43 I think this just emphasises the fact that over 88,000
44 women have been investigated and still there are wide
45 confidence intervals.
46
47 Q. But the confidence intervals would be due to methodology,
48 would they not?
49 A. No, that is due to statistics. Basically, when they
50 analyse the results what they are trying to say is, could
51 this event have occurred by chance? Right? That is what
52 the 95 per cent confidence interval means; it means that
53 in 5 per cent of people investigated it could have arisen
54 by chance, but in 95 per cent of people these are the
55 risks of an increased risk of colon cancer varying from 24
56 per cent up to fivefold. It is really quite an enormous
57 variation.
58
59 MR. JUSTICE BELL: Is that related by some route or other to
60 the fact that during over half a million person years of
