Cluster randomised trials

BMJ 1999;318:1286 ( 8 May )

Letters

Cluster randomised trials

Standardised approach to analysing and reporting these trials is misguided

Authors' reply

Standardised approach to analysing and reporting these trials is misguided

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

EDITOR $---$ In their editorial on cluster randomised trials Campbell and Grimshaw correctly identify the importance of the appropriatechoice of the unit of analysis.¹ Unfortunately, they displaya disappointingly poor grasp of the basis of estimation, and thespecific recommendations that they make areinappropriate.

The authors' plea for a standardised approach to the analysis and reporting of cluster randomised trials is misguided. Theframework that they describe has the patient as the principalunit of the experiment, with the correlation between patientsin the same cluster having to be taken into account in the analysis.Following the recommendations in the editorial may, however, makeinvestigators prey to the same errors that the authors are counsellingthem to guardagainst.

Although some trials fall naturally into the framework that the authors describe, others do not. It is not helpful in theirown example of an educational intervention to implement . . . [Full text of this article]