Cluster-Randomized Trials: Methodical and Practical Implications

Quite often critics demand more randomized studies in rehabilitation science to gather methodological evidence of high quality. However, it is also recognized that the design of double-blind, placebo-controlled, randomized studies often cannot simply be transferred into rehabilitation science. Validity concerning the health care is here in the focus. Thus, treatment as-usual is mostly used as placebo treatment and double-blinding is partly not definable. Additionally, it is often difficult to offer 2 similar forms of treatment in one rehabilitation hospital due to lack of capacity. Additionally, contamination effects are to be expected when patients of different study arms communicate. Here cluster-randomized studies may be helpful. However, in comparison to individual randomized studies they need often higher sample sizes, a more complex methodology of sample size calculation as well as extensive methods of statistical analysis. Within this article advantages and disadvantages as well as the characteristics of cluster randomization are described and information is given how they can be implemented into the field of rehabilitation science.