Published 4 November 2009, doi:10.1136/bmj.b4458
Cite this as: BMJ 2009;339:b4458

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, Tooting, London SW17 0RE

p.sedgwick@sgul.ac.uk

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

To investigate whether physical activity in preschool children (under 5 years) reduced obesity, researchers recruited 545 children from 36 preschool nurseries. Each nursery was randomly allocated to an enhanced physical activity programme plus health education or no intervention (control group). The body mass, physical activity, and sedentary behaviour of each child in each nursery was recorded at regular intervals for 12 months.1

Which one of the following study designs best describes that used in the above study?

a) Case-control study
b) Double blind randomised controlled trial
c) Cluster randomised controlled trial
d) Nested case-control study

c—In a cluster randomised trial, natural clusters or groups of individuals are randomised, rather than individuals. Each preschool nursery was randomly allocated to the enhanced physical activity programme plus health education or no intervention. Within each nursery, children undertook the intervention to which the nursery was allocated. Cluster randomised trials overcome practical and contamination . . . [Full text of this article]


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