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Re: Concrete Ecologic Example Myth
Kai,
No, my comments really had nothing to do with a dose response. I am not sure
you understand the basics of ecologic confounding.
If you want to not believe in the LNT, because you can not explain the inverse
findings from an ecologic study, I have no problems with that. I have
problems with the LNT for non alpha radiation for other reasons.
In Cohen's ecologic study, this is what I see:
1.) An inverse relationship between estimated county smoking information and
estimated county radon concentrations. Maybe the reason for this should be
explored first.
2.) Estimated county smoking rates explaining little of the variation in
county lung cancer mortality.
3.) Uses smoking data that can not adjust for duration of smoking or intensity
of smoking.
4.) Estimated lung cancer incidence rates for the time period of interest
being poorly estimated by lung cancer mortality data from a different time
period.
5.) An inverse association between estimated county radon concentrations and
other smoking related cancers not related to radon, which to me and most
others points to confounding by smoking.
6.) The negative association goes away in Iowa (a state with 1% of the U.S.
population but 1/16 of the U.S. ecologic units) if I merely use better SEER
lung cancer incidence data. Dr. Cohen's only answer for this is that there
must be some problems associated with ethnic minorities in Iowa.
etc.
Given these facts, I am not motivated to perform studies analogous to little
green men.
Perhaps Cohen could set up 1600 ecologic units starting with an inverse
association that he finds between smoking and radon, counties unevenly
weighted by population and geographic area and randomly sample (yes, he would
have to get better data by surveys of counties)the joint distribution of
smoking and related socioeconomic variables in a Monte Carlo analyses?
Email me directly and I would be happy to point you to existing papers that
document points 1-4 below. If you would read the papers that document my
statements below, I think you would understand the limits of ecologic analyses
and the fact it has little to do with dose response.
Bill Field
> Bill,
>
> I think you are confusing trying to establish a dose response relationship
> from ecological data with testing a particular theory against an ecological
> observation. These issues are not limited to epidemiology. It tends to be
> difficult (impossible?) to formulate a theory of how small things interact
> by just looking at the end result of the interaction, but any valid theory
> must still be compatible with the observation.
>
> If I look at Mars and it looks red, that is not proof that Mars is populated
> by a bunch of compulsive Martians who go around painting everything red.
> However, if you have a theory that states that Mars is populated by a bunch
> of compulsive Martians who go around painting everything green, then my red
> observation is a problem for your theory. That doesn't mean your theory is
> wrong, but it would sure help if you could come up with an explanation that
> reconciles your theory with my observation. (e.g. Martians have wives that
> go around covering the green paint up with red blankets.)
>
> To me, no one has come up with an explanation that makes LNT compatible with
> the ecological observation. Until that happens, I can't accept LNT as a
> valid scientific theory. (Using LNT as a basis of regulation is a different
> story.)
>
> You state that many examples have been given on how Dr. Cohen's data can be
> biased. I don't recall any that seem reasonable to me. All I need is one
> NUMERICAL example. Put 1600 hypothetical counties on a spreadsheet. Put in
> some confounders (Martian wives) and reproduce the ecological observation.
> (You correctly state that it may be impossible to IDENTIFY empirical sources
> of ecologic bias from aggregate data alone, but that should not stop you
> from POSTULATING them.)
>
> Kai
>
> ----- Original Message -----
> From: <epirad@mchsi.com>
> To: "Kai Kaletsch" <eic@shaw.ca>
> Cc: "BERNARD L COHEN" <blc+@PITT.EDU>; <radsafe@list.vanderbilt.edu>
> Sent: Friday, June 20, 2003 12:54 PM
> Subject: Concrete Ecologic Example Myth
>
>
> > 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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> >
>
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