Re: LNT models -Constancy of Radon levels over time??

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

On Wed, 8 Mar 2000, Ted de Castro wrote:
> 
> Following this thread I see discussions of confounding factors that are
> difficult to control for because they are non-linear.
> 
> Well the question is this:
> 
> If the end point is "X" and there are multiple possible causal factors
> AND from the end point "X" it is not possible in any way to discern
> WHICH insult was the actual causal factor - HOW is it reasonable to
> accept that the influence of one agent is linear with exposure - and
> another is not?

	--My study avoids the problem of non-linearity by using
"Stratification". For example, if one worries about population density as
a confounding factor, I do a complete analysis utilizing only data from
counties that have nearly the same population density. I do this for many
different population densities, and I always get the same result, without
assuming that anything is linear with population density.
	The reason I am able to do this is because I have 1600 counties in
my data files, whereas 160 counties is enough for doing a complete
analysis with little statistical uncertainty. 
	I also have a treatment of multiple confounding factors, but that
is too complex to summarize here. 


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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