Absence of evidence is not evidence of absence

doi:10.1136/bmj.328.7438.476

BMJ 2004;328:476-477 (28 February), doi:10.1136/bmj.328.7438.476

Editorial

Absence of evidence is not evidence of absence

We need to report uncertain results and do it clearly

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

The title of this editorial is not new. For example, it wasused nearly a decade ago for an article in the BMJ's StatisticsNotes series.¹ Altman and Bland considered the dangers of misinterpretingdifferences that do not reach significance, criticising useof the term "negative" to describe studies that had not foundstatistically significant differences. Such studies may nothave been large enough to exclude important differences. Toleave the impression that they have proved that no effect orno difference exists is misleading.

As an example, a randomised trial of behavioural and specificsexually transmitted infection interventions for reducing transmissionof HIV-1 was published in the Lancet.² The incidence rate ratiosfor the outcome of HIV-1 infection were 0.94 (95% confidenceinterval 0.60 to 1.45) and 1.00 (0.63 to 1.58) for two interventiongroups compared with control. In the abstract, the interpretationis: "The interventions we used . . . [Full text of this article]

Phil Alderson, associate director

UK Cochrane Centre, Oxford OX2 7LG (palderson@cochrane.co.uk)

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