Re: Re: Source of cancer data

["John Williams" <JohnWi@law.com>]

Ruth,



In a case control study, the control of confounding such as smking 

rate and duration is performed at the level of the individual.  The 

interviewer asks each respondent about thir smoking history.  I used 

smoking as an example, but it also relates to other data that is 

collected.  In the ecologic study, Cohen used sales tax to infer 

smoking rates for the county.



  



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