Meta-analysis, done properly, is a systematic effort to search for and
winnow out all the best evidence and show how well a given intervention works.
It is crucially dependent on the identification of all available data from
clinical trials. In 1989, Gøtzsche,1
who was performing a meta-analysis of 244 trials of nonsteroidal anti-inflammatory
drugs in rheumatoid arthritis, drew attention to a practice that seemed to
subvert the normal process of publication as well as of meta-analysis. Excluding
abstracts, letters, and brief versions, Gøtzsche found 44 multiple
publications of 31 of the clinical trials, 20 trials published twice, 10 three
times, and 1 trial 5 times, with the overall proportion of multiple publications
being at least 18%. The fact that the data had been published elsewhere was
not noted in 32 of the 44 articles. Indeed, in about half of them, the first
author and number of authors were different, and in half there were important
discrepancies between the various versions of the same trial. Gøtzsche1 pointed out that "some cases were so difficult to
detect that in a meta-analysis they might have been mistaken for separate
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