RE: Risks of low level radiation - New Scientist Article

["Jim Nelson" <nelsonjima@HOTMAIL.COM>]

Otto,



I read the description here and they go into much more detail regarding the 

shortcomings.



Health Phys 1998 Jul;75(1):11-7





Comment in:

Health Phys. 1998 Jul;75(1):23-8; discussion 31-3

Health Phys. 1999 Mar;76(3):316-9



Comment on:

Health Phys. 1995 Feb;68(2):157-74

Health Phys. 1997 Apr;72(4):623-8



Residential 222Rn exposure and lung cancer: testing the linear no-threshold 

theory with ecologic data.



Smith BJ, Field RW, Lynch CF.



College of Medicine, Department of Preventive Medicine and Environmental 

Health, University of Iowa, Iowa City 52242, USA.



In most rigorous epidemiologic studies, such as case-control and cohort 

studies, the basic unit of analysis is the individual. Each individual is 

classified in terms of exposure and disease status. However, in ecologic 

epidemiologic studies, the unit of analysis is some aggregate group of 

individuals. Summary measures of exposure and disease frequency are obtained 

for each aggregate, and the analyses focus on determining whether or not the 

aggregates with high levels of exposure also display high disease rates. The 

ecologic study design has major limitations, including ecologic confounding 

and cross level bias. Cohen has attempted to circumvent these limitations by 

invoking the linear no-threshold theory of radiation carcinogenesis to 

derive aggregate "exposures" from individual-level associations. He asserts 

that, "while an ecologic study cannot determine whether radon causes lung 

cancer, it can test the validity of a linear-no threshold relationship 

between them." Cohen compares his testing of the linear no-threshold 

relationship between radon exposure and lung cancer to the practice of 

estimating the number of deaths from the person-rem collective dose, 

dividing the person-rem by the number of individuals in the population to 

derive the individual average dose, and then determining individual average 

risk by dividing the number of deaths by the number of individuals in the 

population. We show that Cohen's erroneous assumptions concerning occupancy 

rates and smoking effects result in the use of the wrong model to test the 

linear no-threshold theory. Because of these assumptions, the ecologic 

confounding and cross level bias associated with Cohen's model invalidate 

his findings. Furthermore, when more recent Iowa county lung cancer 

incidence rates are regressed on Cohen's mean radon levels, the reported 

large negative associations between radon exposure and lung cancer are no 

longer obtained.







>From: "Otto G. Raabe" <ograabe@ucdavis.edu>

>To: "Jim Nelson" <nelsonjima@HOTMAIL.COM>, jim.dukelow@PNL.GOV,        

>hflong@pacbell.net

>CC: radsafe@list.vanderbilt.edu

>Subject: RE: Risks of low level radiation - New Scientist Article

>Date: Thu, 06 Dec 2001 14:43:18 -0800

>

>At 09:22 PM 12/6/01 +0000, Jim Nelson wrote:

> >As I told Dr. Cohen a few weeks ago, I agree with the papers by Smith et 

>al.

> >that describe the limitations of Dr. Cohen's work.  The smoking data he 

>uses

> >is so bad, it can only predict a little over 30% of the the lung cancers 

>in

> >the counties. If there was no confounding, it should be able to predict 

>85%

> >or so.  I do not call that good control of confounding.

>**************************************************************

>December 6, 2001

>Davis, CA

>

>Dear Jim:

>

>What do you mean "can only predict a little over 30% of the lung cancers"?

>Do you mean that a regression R2=0.3? If so, that's only a description of

>the fraction of the variability that is explained by the regression. The

>important thing would be whether the trend is statistically significant,

>not that there is considerable excess variability among the data. Such

>variability is to be expected in such a study.

>

>The key point that Prof. Cohen has shown so well is that the disagreement

>between LNT and the observations is extremely robust. It is observed no

>matter how you stratify the data. Just take Colorado as an example.

>Residents of Colorado annually receive among the highest lung doses in the

>U.S. from natural radon and its decay products in the air. Meanwhile,

>Colorado enjoys one of the lowest lung cancer rates in the nation. In 1995

>it was 49 the out of 51. Washington,DC, where radon concentrations are much

>lower, had the highest lung cancer rate in 1995 (Am. Cancer Society, 1996).

>

>Of course, it is always possible to say that some yet-to-be discovered

>cross-level confounder could be causing the "apparent" disagreement with

>LNT, but it does seem unlikely.

>

>Otto

>

>**********************************************

>Prof. Otto G. Raabe, Ph.D., CHP

>Center for Health & the Environment

>(Street Address: Bldg. 3792, Old Davis Road)

>University of California, Davis, CA 95616

>E-Mail: ograabe@ucdavis.edu

>Phone: (530) 752-7754   FAX: (530) 758-6140

>***********************************************





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