7.2.2  Identifying multiple reports from the same study

Duplicate publication can introduce substantial biases if studies are inadvertently included more than once in a meta-analysis (Tramèr 1997). Duplicate publication can take various forms, ranging from identical manuscripts to reports describing different numbers of participants and different outcomes (von Elm 2004). It can be difficult to detect duplicate publication, and some ‘detective work’ by the review authors may be required.


Some of the most useful criteria for comparing reports are:


Where uncertainties remain after considering these and other factors, it may be necessary to correspond with the authors of the reports.