Cluster randomized trials (CRT) are increasingly being used in healthcare evaluation to show the effectiveness of a clinical pathways. In CRTs, patients are nested within clusters such as hospitals and interventions are applied at cluster levels but outcomes are measured at the individual level. It is expected that individuals in the same cluster e.g. hospital, would have more similarities compared to individuals in different clusters. Intraclass correlation coefficient (ICC) is used to determine the degree of within-cluster dependence and it plays an important role in estimating sample size for cluster randomized trials. ICC takes value between 0 and 1. Higher ICC means higher within group similarities compared to between groups similarities. To perform a well-designed cluster randomized trial, the ICC should be available before conducting a trial to estimate the required sample size. The degree of the increase in sample size is a function of both ICC and cluster sizes where generally a greater ICC requires enrollment of a greater number of patients in the trial. In recent years, the need to have published ICCs from different CRTs was put forward to help planning future studies. We are happy to inform you that the first study to present ICC estimates for a cluster randomized trial of care pathway are recently available1.
1 Kul S, Vanhaecht K, Panella M. Intraclass correlation coefficients for cluster randomized trials in care pathways and usual care: hospital treatment for heart failure.BMC Health Serv Res. 2014 Feb 24;14(1):84. [Epub ahead of print]
Assoc. Prof. Dr. Seval Kul
Gaziantep University Faculty of Medicine, Department of Biostatistics, Gaziantep, Turkey