Cohen's Fallacy

["Rad health" <healthrad@HOTMAIL.COM>]

After reading the epidemiologic technique in the paper Dr. Field suggested 

to Dr. Cohen, I think it could possibly help to correct the problem with 

Cohen's analyses pointed out here by Doll and Darby. This is the same 

problem Field pointed out previously of the radon varying more within county 

than between counties.  The variance of smoking within county co-correlates 

with other factors that Cohen has not been able to treat at the within 

county level.



Don



J. Radiol. Prot. 20 (June 2000) 221-222



LETTER TO THE EDITOR



Reply to `Explaining the lung cancer versus radon exposure data for USA 

counties'



Sarah Darby and Richard Doll

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

Clinical Medicine, Harkness Building, Radcliffe Infirmary, Oxford OX2 6HE, 

UK



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.







_________________________________________________________________

Chat with friends online, try MSN Messenger: http://messenger.msn.com



************************************************************************

You are currently subscribed to the Radsafe mailing list. To unsubscribe,

send an e-mail to Majordomo@list.vanderbilt.edu  Put the text "unsubscribe

radsafe" (no quote marks) in the body of the e-mail, with no subject line. You can view the Radsafe archives at http://www.vanderbilt.edu/radsafe/