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Heterogeneity: we can't live with it, and we can't live without it
  1. Frank Davidoff
  1. Correspondence to Dr Frank Davidoff, Institute for Healthcare Improvement, 143 Garden Street, Wethersfield, CT 06109, USA; fdavidoff{at}

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As hard as it is to believe now, it was permissible not long ago to sell a prescription drug (in the USA) without providing evidence that it worked; all that was needed was evidence it was safe. Then, Kefauver–Harris changed everything. Acting largely in response to the thalidomide tragedy, Estes Kefauver, a senator from Tennessee, and representative Oren Harris from Arkansas introduced the amendment that now bears their names. The amendment required convincing evidence of efficacy, as well as safety, before a drug could be brought to market.1 It was signed into law by John F Kennedy on 10 October 1962.

The effect of Kefauver–Harris on clinical practice is unequivocal; its effect on the shaping of clinical evidence has been less obvious. Although it would be hard to prove a strong cause–effect relation between enactment of the amendment and emergence of controlled trials as the evidentiary ‘gold standard,’ the timing is right. Reports of controlled trials that meet reasonable methodological standards began to enter the medical literature in 1948, but their numbers were small until 1966—just a few years after Kefauver–Harris—at which point their …

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