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Ecologic versus case-control



At 01:29 PM 2/11/2002 -0500, Jim Muckerheide wrote:
Bill,
 
I've always agreed that case-control is stronger in principle. But the quality of the study governs. Poor radon studies do not become 'good' because they are case-control; they are still bad statistics, as shown by poor statistics and nearly random variations in results. Large eco study is better than poor case-control. Demonstrated by the statistics and the consistency in results over hundreds of individual studies. Science doesn't depend on the semantics.
 
Jim
--------------------------------

Jim,

I think we found an area of general agreement.    I agree, each study should be judged on its own merits.  There are well performed ecologic studies and case-control studies.  There are also less rigorous ones of each type.  However, even a well performed ecologic study serves only to formulate a hypothesis.  Hypotheses really need to be tested with either a well designed case-control or prospective cohort study.

Also, a study with excellent exposure assessment does not need as large a sample size as one with poor exposure assessment.  Rosner has shown that the more exposure uncertainty you have, the larger the sample size you need to see an association if one exists.   The degree of accuracy in ecologic data versus a case-control study can hardly be judged against the other design.  It is like apples and oranges.  If the ecologic data is very accurate and you know there is no cross-level bias or other non linear dependent factors, an ecologic study can be very accurate on the aggregate level.

Bill

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