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Re: Concrete Ecologic Example Myth
I don't see why any of the discussion below prevents you from
making up a concrete hypothetical example.
Bernard L. Cohen
Physics Dept.
University of Pittsburgh
Pittsburgh, PA 15260
Tel: (412)624-9245
Fax: (412)624-9163
e-mail: blc@pitt.edu
web site: http://www.phyast.pitt.edu/~blc
On Fri, 20 Jun 2003 epirad@mchsi.com wrote:
> Kai,
>
> I know we have gone through discussions about the limitations of ecologic
> studies many times but there are some points that a few radsafers continue to
> miss.
>
> You suggested the other day putting an upper limit on the error from an
> ecologic study. Unfortuantely, this is not easy to do since the error in
> ecologic studies is unbounded.
>
> Others problems to keep in mind -
>
> 1) It is not possible to identify empirical sources of ecologic bias from
> aggregate data alone. Researchers must rely on prior knowledge of intergroup
> variation in the distribution of other risk factors and effect modifiers.
> We don't know this inter group variation for Dr. Cohen's data nor has he
> adjusted for it.
>
> 2) Factors responsible for ecologic bias may not be confounders or effect
> modifiers at the individual level and that identifying the bias is even more
> difficult because factors may not even “appear” to be confounders or modifiers
> at the ecologic level.
>
> 3) Ecologic biases can even reverse the direction of an observed association,
> especially when the range of average exposure levels across groups is small or
> the exposure under study is not a strong risk factor regardless even if you are
> using an ecologic study to test the LNT.
>
> 4) If cross level bias is occurring (which we know it is), ecologic data can
> not be successfully used to adjust for ecologic bias.
>
> Many examples have been given on how Dr. Cohen's data can be biased and since
> Cohen will use his own faulty data to test the "concrete" example; providing
> a "concrete" example is doing no more than providing an explanation Cohen will
> use his own faulty data to negate. So, the circle will never end.
> > Friends,
>
> > We are all aware that ecological studies have some limitations - these issues have been discussed (some would say ad
> > infinitum) on this board and elsewhere.
>
>
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