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OBJECTIVE: To provide insight into current practice in planning for, and acknowledging, the presence of learning and clustering effects, by treating centre and surgeon, when developing randomised surgical trials. STUDY DESIGN AND SETTING: Complexities associated with delivering surgical interventions, such as clustering effects, by centre or surgeon, and surgical learning, should be considered at trial design. Main trial publications within the wider literature under-report these considerations Funded applications, within a four year period, from a leading UK funding body were searched. Data were extracted on considerations for learning and clustering effects and the driver, funder or applicant, behind these. RESULTS: Fifty trials were eligible. Managing learning through establishing pre-defined centre and surgeon credentials was common. One planned exploratory analysis of learning within centre, and two within surgeon. Clustering, by site and surgeon, was often managed through stratifying randomisation, with 81% and 60% respectively also planning to subsequently adjust analysis. One-third of responses to referees contained funder led changes accounting for learning and/or clustering. CONCLUSION: This review indicates that researchers do consider impact of learning and clustering, by centres and surgeon, during trial development. Furthermore, the funder is identified as a potential driver of considerations.

Original publication




Journal article


J clin epidemiol

Publication Date



Clustering, Learning curve, Randomized controlled trials, Statistics, Surgery