Accounting for Cluster Randomization: A Review of Primary Prevention Trials, 1990 through 1993
Judy M. Simpson,
PhD, Neill Klar, PhD, Allan Donner, PhD
American
Journal of Public Health.
1995; 1378-1383
Abstract
Objectives. This
methodological review aims to determine the extent to which design
and analysis aspects of cluster randomization have been appropriately
dealt with in reports of primary prevention trials.
Methods. All
reports of primary prevention trials using cluster-randomization that
were published from 1990 to 1993 in the American Journal of Public
Health and Preventive Medicine were identified. Each article was
examined to determine whether cluster randomization was taken into
account in the design and statistical analysis.
Results. Of the
21 articles, only 4 (19%) included sample size calculations or
discussions of power that allowed for clustering, while 12 (57%) took
clustering into account in the statistical analysis.
Conclusions.
Design and analysis issues associated with cluster randomization are
not recognized widely enough. Reports of cluster randomized trials
should include sample size calculations and statistical analyses that
take clustering into account, estimates of design effects to help
others planning trials, and a table showing the baseline distribution
of important characteristics by intervention group, including the
number of clusters and average cluster size for each group.
Reprints are
available from Judy M. Simpson, PhD, Department of Public Health,
A27, University of Sydney, 2006, New South Wales, Australia.