Re: Cohen's ecological data: a test of LNT?

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

On Fri, 17 Mar 2000, Ken Mossman wrote:

> This my last shot!
> 
> Cohen and I agree that LNT is a causal relationship. Howevever, I am now
> totally confused about whether Cohen's data tests for a causal relationship.
> In his April 1997 paper in Health Physics (page 625), Cohen indicates that
> his data do not test for a causal relationship but has a much more limited
> objective. Now Cohen says that his data tests for a causal relationship.
> Which is  it? Either the data test for a causal relationship or thery don't!

	--It tests for one particular type of causal relationship, namely
Linear-no threshold (LNT). There are many other types of causal
relationships --quadratic, threshold, etc -- and my data do not test for
them or distinguish between them.
	The quote from the page 625 reference above is: "case-control
studies investigate the causal relationship between radon exposure and
lung cancer, whereas our work has the much more limited objective of
testing the linear-no threshold theory". The word "investigate" means
to me "trying to determine". Our work does not, and cannot do this. There
is no implication in my statement that LNT is not a particular type of
causal relationship.

> 
> If the data test for a causal relationship, as Cohen now states, then the
> ecological fallacy becomes operative. If the data do not test for a causal
> relationbship, then the data are not a test of LNT because LNT is a causal
> relationship (as Cohen and I now agree).

	--My data test for the one particular type of causal
relationship,namely LNT, for which the "ecological fallacy does not apply.
If I were to go further and "investigate" what type of causal relationship
is operative, the ecological fallacy would apply, so I cannot do that. I
can only show that LNT does not apply.

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


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