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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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