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Fwd: Re: Cohen's Fallacy
Apologies galore - its just that I did not receive my message from radsafe - so I am sending it out again. I think my message speaks for itself. There is definitely a point for which I address.
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Tom Savin
--------- Forwarded Message ---------
DATE: Sun, 27 Jan 2002 18:06:55
From: "Thomas J Savin " <tjsav@lycos.com>
To: "Rad health" <healthrad@HOTMAIL.COM>
It seems to me that some of this scientific debate is concerned with Type I and type II errors. In other words, does one subscribe statistically to whether or not they are biased to avoid a false positive vs a false negative result. Which camp do they support? Any Comments? Tom
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Tom Savin
On Sun, 27 Jan 2002 16:21:20
Rad health wrote:
>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
>
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