The metawars

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Science  21 Sep 2018:
Vol. 361, Issue 6408, pp. 1184-1188
DOI: 10.1126/science.361.6408.1184

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The number of meta-analyses has exploded the past decade; some 11,000 were published in 2017. The studies, which extract and weigh data from a number of primary studies, have become widely accepted as a standardized, less biased way to answer scientific questions; they are sometimes called the "platinum standard" of evidence and guide thousands of treatment guidelines and social policies. But many meta-analyses aren't the debate enders scientists hoped they would be; often they don't bring clarity but cause more controversy instead. One reason is that, although the basic rules of the meta-analysis are simple, researchers must make many choices along the way, allowing conscious or unconscious biases to creep in.