Study design

doi:10.1136/bmj.b2381

Published 17 June 2009, doi:10.1136/bmj.b2381
Cite this as: BMJ 2009;338:b2381

Endgames

Statistical question

Study design

Philip Sedgwick, senior lecturer in medical statistics

¹ Centre for Medical and Healthcare Education, St George’s, University of London, London SW17 0RE

p.sedgwick@sgul.ac.uk

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

A clinical trial investigated the effectiveness of topical versusoral ibuprofen for chronic knee pain in people over 50. In designinga trial to decide the best treatment approach, which answerbest describes how confounding could be minimised?

a) Double blind trial

b) Intention to treat analyses

c)Matching by age and sex

d) Randomisation of research participants

d—Randomisation means that all individuals have the sameprobability of being allocated to either treatment. Providingthe number of research participants was large enough, randomisationat entry to the trial would ensure no systematic differencesbetween treatment groups in potential confounding factors. Randomisationensures that any differences between treatment groups at theend of the study are only due to differences in treatment andchance associations with confounders. The larger the samplesize, the smaller will be the differences due to chance. Confoundingwould exist if the effect of treatment on . . . [Full text of this article]