The aim of this paper is to describe the design features and practicalities of conducting a cluster randomized trial of obesity management in primary care. The aim of the trial is to assess the effectiveness of an obesity management educational intervention delivered to staff within primary care practices (unit of randomization) in terms of change in body weight of their patients (unit of analysis) at one year. The design features which merit particular attention in this cluster randomized trial include standardization of intervention, sample size considerations, recruitment of patients prior to randomization of practices, method of randomization to balance control and intervention practices with respect to practice and patient level characteristics, and blinding of outcome assessment. The practical problems (and our solutions) associated with implementing these design features, particularly those that result in a time delay between baseline data collection, randomization and intervention, are discussed.
Copyright 2001 John Wiley & Sons, Ltd.