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Re: Cohen's Ecologic Studies





Your postings usually seek to discredit the Cohen study, but they

usually fall short of being understandable.  If you have a clear and

valid point to make, please do so.  Its no good saying there is a

problem without showing clearly what the problem is.



So how about it?  Since you are determined to discredit the study on

Radsafe, make your case clear.  Respond to the question:

------------------------------------------------------

        --Why can't you make up a specific numerical example and show

how

it can affect my results?

------------------------------------------------------

If you can't do that, then I agree with you, "there is no point to

continue this dialog" and you should stop gnawing this bone.  



   _______________________________________________



	Gary Isenhower

	713-798-8353

	garyi@bcm.tmc.edu



epirad@mchsi.com wrote:

> 

> Dr. Cohen,

> 

> It is clear you do not understand the points I am trying

> to make. If you really believe that non linearity of

> confounding has nothing to do with your findings than

> there is no point to continue this dialogue.  After all,

> it is not the first time we agreed to diagree.  I think

> we can both agree on that.

> 

> Lubin has recently given you an example of the problem,

> there is no need for me to repeat it.

> 

> J. Radiol. Prot. 22 (June 2002) 141-148

> 

> The potential for bias in Cohen's ecological analysis of

> lung cancer and residential radon

> 

> Jay H Lubin

> 

> Biostatistics Branch, Division of Cancer Epidemiology

> and Genetics, National Cancer Institute, EPS/8042, 6120

> Executive Blvd, Rockville, MD 20892-7244, USA

> 

> Abstract. Cohen's ecological analysis of US lung cancer

> mortality rates and mean county radon concentration

> shows decreasing mortality rates with increasing radon

> concentration (Cohen 1995 Health Phys. 68 157-74). The

> results prompted his rejection of the linear-no-

> threshold (LNT) model for radon and lung cancer.

> Although several authors have demonstrated that risk

> patterns in ecological analyses provide no inferential

> value for assessment of risk to individuals, Cohen

> advances two arguments in a recent response to Darby and

> Doll (2000 J. Radiol. Prot. 20 221-2) who suggest

> Cohen's results are and will always be burdened by the

> ecological fallacy. Cohen asserts that the ecological

> fallacy does not apply when testing the LNT model, for

> which average exposure determines average risk, and that

> the influence of confounding factors is obviated by the

> use of large numbers of stratification variables. These

> assertions are erroneous. Average dose determines

> average risk only for models which are linear in all

> covariates, in which case ecological analyses are valid.

> However, lung cancer risk and radon exposure, while

> linear in the relative risk, are not linearly related to

> the scale of absolute risk, and thus Cohen's rejection

> of the LNT model is based on a false premise of

> linearity. In addition, it is demonstrated that the

> deleterious association for radon and lung cancer

> observed in residential and miner studies is consistent

> with negative trends from ecological studies, of the

> type described by Cohen.

> 

> URL: stacks.iop.org/0952-4746/22/141

> 

> Regards, Bill Field

> >

> > On Tue, 4 Jun 2002 epirad@mchsi.com wrote:

> >

> > > Dr. Cohen,

> > >

> > > To ignore non-linearity is the root cause of your

> > > findings.

> >

> >       --Linearity of confounding factors has no relevance to my study

> >

> >  In an ecologic analysis you are limited to a

> > > summary statistics to adjust for confounding.  Since you

> > > do not have information on covariates at the county

> > > level, accurate ratio functions cannot be calculated.

> >

> >       --Why can't you make up a specific numerical example?

> >

> >

> > > This becomes very problematic if the data structure is

> > > non linear (e.g. not everyone in the county smokes

> > > cigarettes for the same duration and intensity; not

> > > everyone spends the same amount of time in their home,

> > > not everyone is exposed to the same radon concentration,

> > > etc...), and non additive, which is the case at hand.

> >

> >       --Why can't you make up a specific numerical example and show how

> > it can affect my results?

> >

> > >

> > > I believe the onus is on you to show that multiple non-

> > > linear covariates are not the cause of your problem.

> > > The only way I know you can attempt to do this is use

> > > the methods of Sheppard and colleagues.

> > >

> >

> >       --I never assume anything is linear, except lung cancer vs radon.

> > I need a numerical example to understand what you are talking about.

> >

> > > Lubin has demonstrated the problem in a recent paper

> > > just using smoking.

> >

> >       --My papers give examples of how errors in smoking can explain my

> > results, but then I show that the required correlations are completely

> > implausible. Lubin never addresses the issue of plausibility.

> >

> >  Your inverse associations are found

> > > for other smoking related cancers that should not be

> > > related to radon.  This further strengthens my argument

> > > that your inability to adjust adequately for smoking is

> > > driving your findings.  Or do you believe the reason the

> > > other smoking related cancers also have an inverse

> > > association with your radon concentrations is because of

> > > a hormetic response due to alpha radiation exposure to

> > > the lung?

> >

> >       --I have addressed this in previous messages

> >

> >  I find it far more credible that the

> > > explanation is lack of control of confounding by smoking

> > > and other factors as Lubin has just demonstrated.

> > >

> >       --In BEIR-IV, smoking is not a confounder. Smokers and non-smokers

> > are treated as entirely different species.

> >

> >

> > > You 1997a) claim that simple linear least squares

> > > regression of m on S indicates that nearly all lung

> > > cancer is due to smoking.  However, the results of this

> > > analysis do not support such a claim.  We repeated the

> > > regression of lung cancer mortality rates on your

> > > adjusted smoking percentages.  The resulting R2 values

> > > indicated that S explains only 23.7% of the variation in

> > > lung cancer mortality rates among females and 34.5%

> > > among males.  Puntoni et al. (1995) compared six

> > > mathematical models relating cigarette smoking to lung

> > > cancer risk using data from nine large cohort studies.

> > > They found that 67% of the variation in relative risks

> > > could be explained by a two-stage model of

> > > carcinogenesis.  In comparison, very few of the lung

> > > cancer deaths are explained by your smoking variable.

> > > Therefore, the smoking variable is inadequate to adjust

> > > for the effects of smoking.

> > >

> >       --I have addressed the R-squared issue previously and shown that

> > it is irrelevant

> >       --I have also shown that any choices of the smoking prevalences in

> > the various counties that are not completely implausible would not affect my

> > results.

> >

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