Re: Ecologic LNT study - reply from Dr. Lubin

[Bernard L Cohen <blc+@pitt.edu>]

	I have treated many potential correlations between relavant
factors for individuals. Of course, I have not treated every possible one,
and that is why I am seeking suggestions for others that should be
treated.
	With all the general problems cited with my analysis, it should be
easy to pick a potential specific explanation for my results that is
overlooked or improperly treated by my analysis. It doesn't have to be a
correct explanation; it only has to be an explanation that I cannot show
to be highly implausible -- the burden of proof is on me. All you have to
do is propose a potential specific explanation, and if I can't show that
it is very highly implausible, I will concede.

Bernard L. Cohen
Physics Dept.
University of Pittsburgh
Pittsburgh, PA 15260
Tel: (412)624-9245
Fax: (412)624-9163
e-mail: blc+@pitt.edu


On Mon, 6 Mar 2000 FIELDRW@aol.com wrote:

> This exchange has been very useful.  The fundamental disagreement that I have
> with Dr. Cohen is simply whether one can "scale up" a model for individuals 
> and
> attain a meaningful model at the county level.  The answer is no; one cannot
> "scale up" without accurate within-county information on risk factors (and the
> county-to-county variation) - information that ecological studies do not have.
> Let's state the issue in the reverse.  Suppose several counties have equal
> county-level radon "means", and equal county-level data for all other risk
> factors (the same mean ages, proportion of smokers, SES, etc), i.e., at the
> county level the covariate information is identical across counties.  Is there
> anything that can be inferred about the lung cancer rates in the counties?  
> The
> answer is no; one cannot draw any logical inference about the lung cancer 
> rates
> in the counties.  While the risk factor information is the same at the county
> level (and thus no additional adjustments are ever possible using county
> information), differences in lung cancer rates at the county level may occur 
> due
> to differences in the correlational relationhips among the risk factors within
> the counties.
> 
> Population dose can be a valid indicator of population risk, and "scaling up"
> can be valid only when the risk relationship between disease outcome and all
> risk factors is linear in all risk factors.  However, there is overwhelming
> evidence that the functional relationship between radon, other risk factors 
> and
> lung cancer is most decidedly not linear - it is linear in radon exposure, but
> proportional to the background rate.  This non-linear relationship for risk 
> has
> been most clearly demonstrated in the greater than additive associations 
> between
> radon and numerous factors and lung cancer, such as radon and tobacco use (and
> very likely exposure to environmental tobacco smoke, but this has not really 
> be
> explored), radon and attained age, radon and gender (only suggestive data),
> radon and previous lung diseases, and radon and other mining exposures (in
> populations occupationally exposed to radon).  Analyses have consistently
> demonstrated a linear relationship between lung cancer and the excess relative
> risk.  That functional form implies that conditional on other risk factors, 
> lung
> cancer risk increases proportionally to the background rate with increasing
> radon progeny exposure.  While the relative risk may be linear, the absolute
> excess risk with increasing exposure is dependent on the myriad of other risk
> factors. This is the reason that even though counties may have equal (or 
> greater
> or lesser) radon concentrations, county lung cancer rates cannot be "scaled 
> up"
> with any validity and be compared without information (at the level of
> individual) on other lung cancer risk factors.
> 
> My problem is then with ecological studies.  I do accept that it is a 
> perfectly
> valid scientific question to ask whether there is an excess risk of lung 
> cancer
> at the lowest levels of (residential) radon progeny exposure - but for
> individuals.  In my view, the data are consistent with some excess risk at the
> lowest exposures, but I will allow that this is an arguable proposition.
> However, ecological analyses shed no light on this issue, since one cannot
> "scale up" with validity.
> 
> Jay Lubin
> 
> Jay Lubin, PhD
> National Cancer Institute
> Biostatistics Branch, EPS/8042
> 6120 Executive Blvd
> Bethesda, MD 20892-7244
> Tel: 301-496-3357
> Fax: 301-402-0081
> Email: lubinj@exchange.nih.gov <mailto:lubinj@exchange.nih.gov> 
> -----------------------------------
> Bill Field
> mailto:bill-field@uiowa.edu
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