The Cochrane Collaboration Insists on Finding Every Study, Not Just the Convenient Ones

A systematic review exhaustively searches for and critically appraises every study addressing a specific question, following a pre-specified, published protocol for what counts as an eligible study and how its quality is judged, rather than relying on a reviewer's own selective reading of the literature they happen to know. The method was institutionalized in 1993 with the founding of the Cochrane Collaboration, an international network built explicitly to produce and maintain systematic reviews of medical evidence to a fixed, replicable standard, in response to the recognition that ordinary narrative literature reviews were prone to citing whichever studies supported a reviewer's prior view.

Claims that a religious practice produces a measurable benefit, on health, wellbeing or behavior, are frequently supported in public discussion by citing a handful of favorable studies while ignoring a larger number of null or unfavorable ones that a systematic search would also have found. The atlas treats a properly conducted systematic review of a practice's claimed effects as stronger evidence than any individual study it might cite, precisely because a systematic review's protocol requires searching for and reporting the unfavorable evidence too.