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The Cochrane Collaboration should be congratulated for its dedication to documenting continuing clinical trials, teaching critical appraisal, and supporting research into new methods of reviewing the literature. However, Cochrane Reviews can be created by untrained people who simply follow an algorithmic approach and are unaware of important methodological issues. Therefore, the objective of this article is to highlight important limitations of Cochrane Reviews, including the Review Manager software1 that is required,2 the inappropriate use of a summary statistic, and finally the restriction to only randomised controlled trial (RCT) data. To illustrate these points, I have used a 1% random sample of Cochrane Reviews—that is, 16 studies numbered 1, 101, 201…1501 of 1596 of the Cochrane Database on 3 April 2003.3–18
LIMITATIONS OF THE COCHRANE APPROACH
There are important limitations to the software required by the Cochrane Collaboration (Review Manager). Most important is that Review Manager cannot include (a) results based on survival analyses—for example, most appropriate analysis for time to next injury—and instead calculates relative risks based on simple proportions (this leads to inappropriate estimates when patients have different lengths of follow up19) and (b) analyses adjusted for confounding—that is, multiple regression analysis. Software is available, but requires statistical expertise that would preclude the algorithmic approach.
Whereas the Cochrane Collaboration could improve its software, the other two major problems are process oriented. The Cochrane Collaboration promotes wide participation, and this leads to inexperienced authors and peer reviewers. For example, it is not always appropriate to pool data into one overall summary statistic,20 and, even when it is, there are different methods—that is, fixed and random effects models—to be used depending on the structure of the data.20,21 In the …