Re: LNT and Collective Dose

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

On Wed, 13 Feb 2002, Field, R. William wrote:



> Dr. Cohen,

>

> Do you agree with the definition below for ecologic fallacy and my points

> below (especially number 6) below in response to Ruth's question?

>

>

>       Ecologic fallacy is merely an inappropriate conclusion

>       regarding relationships at the individual level based on

>       ecological data (Kelsey et al. 1986).



	--There are many definitions of the ecological fallacy, but names

are not important



>

>       However, ecologic studies inherently have many weaknesses that

>       lead to an inappropriate conclusion.



	--I have offered to show how any other published ecological study

can give a misleading conclusion. I could do this in less than an hour,

but for my study, I have not been able to do it after 7 years of trying.

The major difference is that all other studies are trying to determine a

dose-response relationship, and an ecological study is not capable of

doing that. My study is a test of the linear-no threshold theory which is

a very different thing.

	For such a test, there are problems which are different than the

problems with case-control studies, but I don't like the word "weakness".



>       1) in case-control studies nondifferential (or random error)

>       exposure misclassification usually causes bias toward the

>       null.  However, in an ecologic study nondifferential

>       misclassification can drive either sizable under or over

>       estimation of the exposure disease relationship.



	--You have to give me a specific example to discuss this



>

>       2) Using summary measures (like sales tax to represent smoking

>       prevalence) for a county is very inadequate to control for

>       confounders.



	--In my study, I don't "control" for anything. To me, "control

for" means using multiple regression analysis which is fraught with peril.

I believe I have amply demonstrated that uncertainties about smoking

cannot help substantially to explain my data. Your reference to "sales

tax", which was not my primary source, gives me the impression that you

have not read my papers on that subject.



>       3) Some factors that are not confounders at the individual

>       level can be at the ecologic level.  To have any hope of

>       control for confounding at the county level, you need very

>       detailed information on the confounding and exposure variable

>       distributions within a county.  That is why I previously

>       suggested to Dr. Cohen that he try to obtain this information

>       (method suggested by Guthrie).



	--The only way to discuss confounders i with specific examples.

Unless you are willing to suggest a specific example, Ican't discuss that

subject beyond what is in my papers, especially the paper on "Treatment of

confounding factors in an ecological study" which is posted on my web

site.



>       4) Jim Muckerheide often cites the large numbers of counties in

>       Dr. Cohen's studies.  But, the availability of large numbers

>       does not eliminate biases no matter if you had an infinite

>       number of counties.  Large numbers do help improve the

>       precision (narrow confidence bands), but the large numbers have

>       no effect on reducing biases.  In other words, the finding can

>       be precisely wrong.



--I have never claimed that my good statistics eliminates biases





>       5) I have seen no data from Dr. Cohen to show that the risk

>       factors within counties are not correlated.  Unless the risk

>       factors are purely additive (and I see no evidence of that),

>       the dose response findings for the ecologic study will be

>       biased.



	--I have never claimed that risk factors are not correlated, and

have treated examples where they are correlated



>       6) Ruth, in your example below, the population is not at all

>       defined so the concept of collective dose and collective risk

>       can not be used.  Collective dose and collective risk can only

>       begin to be considered valid if the exposed population can be

>       well described and quantified.   For example, many groups of

>       workers who may have a higher risk of exposure can be

>       quantified by age, job description, sex, length of employment

>       and a multitude of other factors.  The general (working) group

>       I described above has many more demographic details than is

>       available in ecologic studies.  If you don't have better

>       demographics than are available in a county ecologic study, you

>       likely should not be using the collective dose concept.



	--According to the BEIR Reports, it is easy to show that

collective doses determine the number of deaths. This is a property of

LNT. Of course, some care is necessary in handling other factors--

collective dose to what group of people, ages, sex, etc. --

but health physicists and risk assessors have been doing this for decades.



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