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 the results of epidemiological studies and try to convey their meaning to others. This is not an easy task, as is illustrated by the recent "pill scare" in the United Kingdom, in which there was much confusion over the clinical importance of the scientific information that was made public. Furthermore, practising clinicians also need a readily understandable tool for weighing the risks of various treatments. Ideally, this should be feasible without recourse to complicated statistical concepts. In this paper, we propose a simple and intuitively understandable method for expressing the 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 effects of a treatment. These will often (at least for pharmacological interventions) have been established in randomised controlled trials . . . [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]

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