Considering cluster analysis in sport medicine and injury prevention research.

Objective: In the field of sport medicine and injury prevention in sport, prospective study designs implementing cluster randomization or grouping of subjects by cluster (ie, team, clinic, school, community) are becoming increasingly common. However, there are very few published studies in the field that adequately account for clustering effects in the design and analysis, leading to potentially spurious conclusions. This paper will review the implications of using a cluster RCT or other intervention or observational design grouping individuals by cluster and to highlight the practical implications of appropriate analysis considering the effects of clustering.
Data Sources/synthesis: Previously published papers have provided a foundation of expertise to discuss the often neglected impact of ignoring the effects of cluster in the design and analysis of cluster RCT and other study designs that group individuals by cluster in sport medicine.
Results: The loss of statistical efficiency inherent when a study design implements randomization or grouping by cluster is reviewed. Specifically, the effect of cluster design on sample size considerations and analysis are discussed in the context of data from a recently published cluster RCT examining the effectiveness of a balance training prevention strategy in youth basketball.
Conclusions: Researchers in sport medicine are encouraged and challenged to consider appropriate research design and analytical techniques more consistently when study subjects function in the context of a cluster in order to avoid spurious results and misleading conclusions.