Dan
Thanks for your simplification of this complicated issue.
Previously, I have taught that a diagnostic test study with an
undifferentiated group of subjects (similar to the population one for which
one would use the test) is more valid (at least external validity) than a
similar study using the extremes (known disease and known health).
Describing these as cohort and case-control studies is very helpful in this
context, and parallels the evidence hierarchy in other study conclusion types.
Brian
Brian S. Alper MD, MSPH
Editor-in-Chief, DynaMed (http://www.DynamicMedical.com)
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