Re: RE: Field's comments on Cohen's Observation

[BERNARD L COHEN <blc+@PITT.EDU>]

On Mon, 23 Jun 2003, Gary Howard wrote:



> I think I understand this from what Dr. Fields tried to explain to us

> before, I think he means that while lung cancer incidence and radon

> exposure are linear in the relative risk according to the LNT, they

> are not linearly related in the scale of absolute risk.



	--Can you explain this in more detail? To me, LNT means that the

increased risk from radon is linearly proportional to radon exposure. This

refers to absolute increased risk; what do you mean by relative risk?



> This is what Doctor Jay Lubin at the NCI pointed out so eloquently in

> his his last paper concerning Dr. Cohen's work.



>  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.



	--I never said that. Item #7 on my web site is full of my

treatments of confounding factors.



 These assertions are erroneous. Average dose

> determines average risk only for models which are linear in all

> covariates,



	--I never assume risks to be linear in any co-variates. Using

stratification avoids that. Case-control studies make wide use of

multivariate regression which usually does assume linearity.



 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.



	--This is what I don't understand. As requested above, I hope you

will explain it to me.



> 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.



	--These are easily explained by confounding factors that are not

considered. In my studies, I have given very extensive consideration to

confounding factors.



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