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I read with very great interest David Sackett’s letter. He concludes
that a-priori-probabilities (or a-priori-hunches) of efficacy influence
the test for successful blinding. I retain: apparently a-priori-
probabilities of efficacy do exist. There are two items I want to point
Item 1: A-priori-probabilities of efficacy are also closely related
to a-posteriori-probabilities of efficacy. Thus, David Sackett provided an
important example showing that Bayesian interpretation (rather than
hypothesis testing) of a trial is not only necessary but also feasible.
Item 2: A-priori-probabilities were not balanced in David Sackett’s
example (and probably in many other trials as well). Is it than still
ethical to conduct a randomised trial in which patients are allotted to
treatment that is a-priori felt to be inferior?
David L. Sackett: BMJ 2004;328:1136 (8 May),
No competing interests
02 September 2005
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