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Re: Concrete Ecologic Example Myth





On Sat, 21 Jun 2003 epirad@mchsi.com wrote:



> In Cohen's ecologic study, this is what I see:



	--I have responded to all of these point in the last few days. If

anyone wants repeats of one of these responses, please specify

>

> 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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