Day 256 - 04 Jun 96 - Page 44


     
     1        between the intake of animal fat and breast cancer in
     2        China, according to this passage and the rest of your
     3        study, is weak, is it not?
     4        A.  It is significant.
     5
     6   Q.   But how significant?
     7        A.  It is quite significant.  It is statistically -- there
     8        is less than one chance in 20 that this is a chance
     9        observation.
    10
    11   Q.   Can I ask a question about that.  Do you use relative risks
    12        in expressing the magnitude of risk?
    13        A.  In certain kinds of analyses yes.
    14
    15   Q.   Would you use them for this kind of work?
    16        A.  I have forgotten exactly, this paper here, whether we
    17        did or did not.  This was actually a paper -- this was
    18        referring to a paper that was done by my colleagues at
    19        Oxford here in England, as well as in London.  When we do
    20        basically all case control studies, you are comparing case
    21        versus controls, then of course we use relative risk as the
    22        sort of outcome, but not when we are doing sort of ecologic
    23        comparison; we do not use that term.  But in this case
    24        I think we did use relative risk, but I cannot -----
    25
    26   Q.   This is a slight red herring, Professor.  Do you have a
    27        knowledge of case control studies and the way that their
    28        results are expressed?
    29        A.  Yes, I do.
    30
    31   Q.   Do you agree that, at any rate, so far as a case control
    32        study is concerned, a relative risk of less than about
    33        threefold is not worth bothering about, save as the genesis
    34        of a hypothesis?
    35        A.  No, I do not agree.  For example, if we have a relative
    36        risk of 1.6 or 7, it does not sound like much, or even 2 or
    37        so, it does not sound like much, but if it is statistically
    38        significant and repeated and repeated -- replicated, if you
    39        will -- in other words, we have confidence that it really
    40        is one and a half or two-fold or so, if it is a disease
    41        that is common, then the total number of cases of course
    42        can be quite significant.  So we have to confess that even
    43        that relative risk is significant.
    44
    45   Q.   My fault entirely.  I meant for a single study, properly
    46        conducted with a sound methodology, a relative risk which
    47        came out at less than about 2 would not be significant?
    48        A.  Probably so, yes.
    49
    50   Q.   How far in the other direction do you go, if you take the 
    51        standard or basis as 1, how far in the other direction do 
    52        you go, for example, in a case control study, before you 
    53        say there is a negative or inverse association?
    54        A.  Those two words mean something different; negative and
    55        inverse mean something very different.
    56
    57   Q.   I am sorry.  Use inverse.
    58        A.  OK.
    59
    60   Q.   Protected, if you like?

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