The controversies over salt have forced to the foreground critical methodological questions that are too often masked by the universal conviction that clinical practice and public policy must be evidence based. Sometimes indirectly, sometimes explicitly, those engaged in the salt debate have raised questions about the role of randomized controlled trials as the source of definitive evidence and about the relative importance of systematic reviews in general and Cochrane reviews in particular. Advocates of salt reduction have sometimes asserted that the “weight of all the evidence”—including data from observational studies, animal experiments, and clinical experience—should trump the results of analyses that weigh only randomized controlled trials. Insistence on gold-standard evidence would place policy makers in methodological straitjackets and result in policy paralysis. Findings that did not meet the most exacting standards of science might be more than adequate for the purposes of setting policy.
The whole article, by Ronald Bayer, David Johns, and Sandro Galea (most recent Health Affairs), is worth reading.