Linearity of covariates and radon exposure - response to Mr. Sonter

[epirad@mchsi.com]

Dr. Howard, thanks for responding perhaps more clearly then I could regarding 

Mr. Sonter's comment.  



Mark, 



I placed a copy of Dr. Lubin's paper in the mail.  Please email me directly if 

anyone else would be interested in a copy of the paper. Also, if anyone has 

comments, please email directly so we can take the discussion off list. 



I have also attached a copy of the Darby and Doll letter (from Journal of 

Radiologic Protection) below, perhaps they can present the points I attempted 

to make a bit clearer and from a different perspective. 



Regards, Bill Field

epirad@mchsi.com



"Explaining the lung cancer versus radon exposure data for USA counties"



Dear Sir



Professor Cohen states in his letter that his analysis ‘encompasses all of the 

Doll suggestions’. It is, however, logically impossible for it to have done so 

using data at the level of counties. This is because the effect of cigarette 

smoking on the relationship between residential radon and individual lung 

cancer risk will be determined by the relationship between smoking status and 

lung cancer among the individuals within each county. Unless smoking is 

irrelevant to lung cancer risk (which we know to be untrue) or smoking status 

and residential radon are uncorrelated within each county (which seems 

unlikely), the relationship between residential radon and lung cancer at the 

county level will differ from that at the level of the individual in a way 

that cannot be overcome by including corrections for smoking habits at the 

county level, even if these corrections correctly represent the smoking habits 

of the individuals within each county. The difference in the relationship 

between a risk factor and a disease rate at the level of the individual and at 

an area level is the ecologic fallacy and is described in detail by Greenland 

and Robins (1994) and Morgenstern (1998). Lubin (1998) has also demonstrated 

that biases caused by the ecologic fallacy can be of any magnitude from minus 

infinity to plus infinity. In two recent studies (Lagarde and Pershagen 1999, 

Darby et al 2000), parallel individual and ecological analyses have been 

carried out of identical data from case-control studies of residential radon 

(Peshagen et al 1994, Darby et al 1998). These analyses have shown that, in 

addition to any bias caused by the ecological fallacy, ecological studies of 

residential radon and lung cancer are also prone to biases caused by 

determinants of lung cancer risk that vary at the level of the ecological unit 

concerned. In these two examples, the additional variables were latitude and 

urban/rural status respectively. The explanation of these variables is not yet 

well understood and they may well be, in part, surrogate measures for some 

aspects of the subjects’ smoking history not accounted for by the measures of 

smoking status that have been derived from the individual questionnaire data 

and used in the analysis of the data for individuals. They had only a minor 

effect on analysis at this level but a substantial effect on the ecological 

analyses. The presence of these variables is further evidence of the pitfalls 

of ecological studies.





Yours faithfully,

Sarah Darby and Sir Richard Doll

Clinical Trial Service Unit, University of Oxford, Nuffield Department of 

Clinical Medicine,

Harkness Building, Radcliffe Infirmary, Oxford OX2 6HE, UK

-----------------------

> 

> On Mon, 23 Jun 2003 10:42:05 +1000 Sonter Mark

> (sonterm@epa.nsw.gov.au) wrote:

> 

> Yuo say that "radiologically induced lung cancer is not linearly

> related to dose in person-rems" ---  BUT THAT IS PRECISELY WHAT THE LNT

> HYPOTHESIS DECLARES, without qualification.

> 

> If it's not so, fine, but then the LNT is not true!!!!

> 

> Mark Sonter

> 

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