Day 106 - 23 Mar 95 - Page 55
1 one test per consignment, say they do 17 tests a day,
2 something like 5,000 tests a year, if, as has been stated,
3 they found E.coli 0157 twice since sampling was started
4 about four years ago, what does that suggest to you about
5 the possible presence of E.coli 0157 in terms of twice out
6 of 5,000 or something?
7 A. None at all. You cannot extrapolate at all one way or
8 t'other. All it says is out of those two consignments they
9 found it. It means essentially they landed on it
10 accidentally. You could say that in those particular
11 batches that it was high level, but an equal inference is
12 that they blundered on it. Unless you set up a
13 mathematically designed sampling programme on a truly
14 random basis you cannot extrapolate results. Your results
15 have no meaning for the purposes of extrapolation. You
16 cannot and must not draw conclusions from them. There is
17 no validity. It is useless information. All it tells you
18 is on that day when you took that sample you found it.
19 This is the trouble, because the nature of "random" is very
20 poorly understood in general. "Random" does not mean, oh,
21 picking here, here and here. It does not mean a person
22 going in with the cutter and dunking it in where they feel
23 like it. That is not random. Every person, whether they
24 realise it or not, may be guided by their own inherent
25 pattern; they make take it there, there, there. That is
26 not strictly random.
27
28 To set up a three-dimensional random sampling programme is
29 incredibly complex, because you have to do in it 3-D. What
30 you would practically, there are several ways of doing it,
31 but the way I would approach that is you would draw a grid
32 over the box and then a vertical grid, so that you had a
33 number of boxes. You would allocate each of those a number
34 and then you would run those through either a computer to
35 give you random numbers or through random number tables so
36 you had a box selected totally at random which you would
37 then sample.
38
39 Q. Are you suggesting that it is something that could be done
40 once in a while?
41 A. Well, where -- I mean, in the real world, where
42 obviously that type of sampling is expensive and
43 disruptive, I tend when I am involved in this sort of work
44 to put my money into sampling of very few batches very
45 intensively, rather than sampling a large number of batches
46 in a vague distribution. I would tend to link it to
47 setting up operations, but in terms of making claims which
48 we have seen in Mr. Walker's, or satisfying expectations
49 vis-a-vis McDonald's as to product being free from X-Y-Z,
50 the sampling programme conducted does not enable the
51 supplier of that product to make any such assurance.
52
53 Q. So if Mr. Walker said in his evidence that the meat was
54 free from E.coli 0157, what is your conclusion on that?
55 A. If he said that, and I am not sure he did say that,
56 I think he said that McDonald's expected it to be free from
57 0157, all one can say of that is that McKey's have no way
58 of knowing whether or not it is free from 0157 and are not
59 carrying out any scientifically based programme which would
60 enable them to give any such assurance. In fact, the only
