Expressing the magnitude of adverse effects in case-control studies: "the number of patients needed to be treated for one additional patient to be harmed"

doi:10.1136/bmj.320.7233.503

BMJ 2000;320:503-506 ( 19 February )

Education and debate

Expressing the magnitude of adverse effects in case-control studies: "the number of patients needed to be treated for one additional patient to be harmed"

Lise M Bjerre, doctoral candidate ^a, Jacques LeLorier, chief ^b.

^a Department of Epidemiology and Biostatistics, Faculty of Medicine, McGill University, Montreal, Canada H3A 1A2, ^b Pharmacoepidemiology and Pharmacoeconomy Research Unit, Centre de Recherche, Centre Hospitalier de l'Université de Montréal, Campus Hôtel-Dieu, Montreal, Canada H2W 1T8

Correspondence to: J LeLorier leloriej@ere.umontreal.ca

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

The need to express estimates of risk in an understandable manner is a challenge faced regularly by those who work with theresults of epidemiological studies and try to convey their meaningto others. This is not an easy task, as is illustrated by therecent "pill scare" in the United Kingdom, in which there wasmuch confusion over the clinical importance of the scientificinformation that was made public. Furthermore, practising cliniciansalso need a readily understandable tool for weighing the risksof various treatments. Ideally, this should be feasible withoutrecourse to complicated statistical concepts. In this paper, wepropose a simple and intuitively understandable method for expressingthe results of case-control studies.

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Evidence from randomised controlled trials

Any intervention or exposure may have desirable and undesirable effects. Desirable effects are usually the intended effectsof a treatment. These will often (at least for pharmacologicalinterventions) have been established in randomised controlledtrials . . . [Full text of this article]

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Rapid Responses:

Read all Rapid Responses

NNT has no merits.: J L Hutton
bmj.com, 22 Feb 2000 [Full text]
Number needed to treat: an oversimplified interpretation of research findings: Zhiqiang Wang
bmj.com, 15 Mar 2000 [Full text]
Authors' reply to Dr J L Hutton's response: Lise M Bjerre, et al.
bmj.com, 23 Mar 2000 [Full text]
Authors' reply to Dr Z Wang's response: Lise M Bjerre, et al.
bmj.com, 12 May 2000 [Full text]
Expressing the number needed to treat as a function of the odds ratio and the unexposed event rate: Ralf Bender
bmj.com, 7 Nov 2000 [Full text]