BMJ  2007;334 (17 February), doi:10.1136/bmj.39126.301019.3B

Editor's Choice

Editor's choice

Controversies revisited

The first 150 words of the full text of this article appear below.

Last September Malcolm Potts and colleagues caused a small furore in our rapid responses by suggesting that some interventions were so obviously effective that they did not need evidence from randomised controlled trials (2006;333:701, doi: 10.1136/bmj.333.7570.701). Correspondents took them to task over their specific examples (misoprostol for postpartum haemorrhage and circumcision for preventing HIV transmission, but, interestingly, not for oral rehydration therapy) or simply for arguing that "obviousness" was a reasonable criterion.

This week Paul Glasziou and his colleagues tease out some criteria for when observations may speak for themselves (doi: 10.1136/bmj.39070.527986.68). Their analogy is that of the signal to noise ratio: "how much difference between the treatment outcome (signal) and the natural outcome (noise) is enough? We know that confounding is common and often not obvious; indeed, this was the basis for inventing randomised controlled trials." But there may be some cases where the signal is strong . . . [Full text of this article]

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