RADON - Ecologic Studies

["R. William Field" <bill-field@uiowa.edu>]

Dr. Cohen,

I truly understand that you want someone to make a suggestion in
quantifiable terms that offers an explanation for your findings.  That is
why we took the time to address your requests in the past.  

It is my opinion, that people have offered very plausible examples to
explain how an inverse associations can occur.  I do not think you should
always expect a scientist to continue following up every rebuttal you
offer.  Maybe, they thought they made their case with their initial
presentation and that no follow-up to your rebuttals were necessary.
People have other commitments other than reviewing your research or
rebutting your claims.

The factors that are causing your inverse association may be
unidentifiable, do you understand that?  

Greenland and Morgenstern have shown that extraneous risk factors
responsible for ecologic bias may not even be confounders or effect
modifiers at the individual level.  So in all cases, you may not be able to
describe the bias in quantifiable terms.  Do you understand this?

Further, The problem of identifying the bias is made even more difficult by
the fact that factors responsible for ecological biases may not even APPEAR
to be confounders or modifiers at the ecologic level.

There will be no bias in an ecologic study if both the background (rate of
disease) and the exposure effect do not vary across groups, and there is no
confounding within groups.  Small departures from these conditions result
in substantial bias, even reversing the direction of the observed
observation.  
   
For other radsafers - I highly recommend the paper by Greenland and
Morgenstern on this topic, (International Journal of Epidemiology
18:269-274, 1989).

Dr. Cohen - I have 2 direct questions for you.  I hope you can give me a
direct answer. 

You apparently have been trying to find the reason you are finding an
inverse relationship in your data for many years.  You have not been able
to find a reason. 

1) Do you truly believe that if no one else can offer a explanation for
your findings (that is an explanation that is acceptable to you), then your
findings have the required validity to scrap the LNTT?   

2) Is there ANY chance that your inverse ecologic findings can be
attributed to aggregation or specification bias?

Dr. Cohen - My criticisms concern your methods, not you.  Please do not
take any of  my comments as an ad hominem attack.

Bill Field
bill-field@uiowa.edu


******************************
R. William Field, Ph.D.
Division of Epidemiology
Department of Preventive Medicine
  and Environmental Health
N222 Oakdale Hall
University of Iowa
Iowa City, Iowa 52242
319-335-4413 (phone)
319-335-4747 (fax)
mailto:bill-field@uiowa.edu
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