LNT model question

[FIELDRW@aol.com]

Dr. Cohen wrote concerning the question I posed:  "My derivation of the 
formula I was testing is given in my paper in Health Physics 68:157-174;1995. 
The mathematical derivation is given in Sections B and C, and in the lengthy 
mathematical Appendix A. Can you suggest where this derivation falls short of 
being convincing? This derivation starts with the BEIR-IV formula for risk vs 
dose to individuals, and develops a prediction of lung cancer rates vs 
average radon levels for counties."
 
Field Response: As we suggested before (see references below), the risk model 
you derive from the BEIR IV model is not equivalent to the BEIR IV risk 
model.  You attempted to equate the model to the BEIR IV model by applying 
rigid assumptions that include: 1) The time spent in the home is the same for 
all individuals; 2) radon exposures occurring outside the home do not 
contribute to lung cancer risk; 3) baseline lung cancer mortality is solely a 
function of age and smoking; 4) all smokers have the same increased risk of 
mortality; 5) smoking duration and intensity is the same for everyone; 6) age 
is the only modifying effect of radon exposure; and 7) radon concentration is 
directly proportional to the delivered dose from the radon progeny.  Your 
relative risk model is only valid if these assumptions are not violated.  You 
previously have  attempted in your published manuscripts to support your own 
primary assumptions by use of secondary assumptions or qualifying statements 
like: 1) "On average, people spend 75% of their time in the home…"; 2) "… 
average radon levels are generally much higher in homes …"; 3) "….. 
workplaces of various counties would strongly tend to be proportional ….." ; 
4) "….. it is generally agreed that radon gas level is a much better 
indicator than WLM of radiation dose in homes …."; and 5) "This crudely 
introduces the pack-years concept".  The very foundation of your assumptions 
that you use to equate your risk model to the BEIR IV Risk Model is based 
further on poorly documented assumptions.  The assumptions all have both an 
error associated with them and a very significant NON-LINEAR component, which 
as previously pointed out, can not be quantitatively described.  The BEIR IV 
model, unlike your model, is not confined by either your primary or secondary 
assumptions.     

Smith, B.J., Field, R.W., Lynch, C.F., Residential Radon-222 and Lung Cancer: 
Testing the Linear No-Threshold Theory with Ecologic Data. Health Physics. 
75(1): 11-17, 1998.  

Field, R.W., Smith, B.J. and Lynch, C.F. Ecologic Bias Revisited, A Rejoinder 
to Cohen's Response to "Residential Radon-222 Exposure and Lung Cancer: 
Testing the Linear No-Threshold Theory with Ecologic Data". Health Physics, 
75(1): 31-33, 1998.  

Field, R.W., Smith, B.J., and Lynch, C.F. Cohen's Paradox, Health Physics 
77(3):328-329, 1999.
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Dr. Cohen wrote - "This correlation is favorable for verifying LNT. If 
smoking  rates were positively correlated, my correction for smoking would 
have  increased the discrepancy with LNT. The negative correlation I adopted  
reduced the discrepancy. The effects of various assumed correlations  between 
smoking prevalence and mean radon levels are presented in my 1995  paper. If 
the negative correlation were perfect, the discrepancy with LNT would have 
been cut in half."  

Field Response:  My question regarded why you felt you found such a strong 
inverse association between mean county radon concentrations and your 
estimated county smoking rates.  I do not think this can be explained merely 
by an urban/rural phenomenon.  It would be interesting to see if this inverse 
association held for living area measurements, rather than basement 
measurements.  Dr. Naomi Harley has previously shown that for the midwest, 
basement radon concentrations do a poor job of predicting overall radon 
exposure. First floor living area measurements do a much better job.

Bill Field

-----------------------
R. William Field, Ph.D.
College of Public Health
N222 Oakdale Hall
University of Iowa
Iowa City, Iowa 52242

319-335-4413 (phone)
319-335-4748 (fax)
mailto:bill-field@uiowa.edu
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