Effect of imbalance and intracluster correlation coefficient in cluster randomization trials with binary outcomes when the available number of clusters is fixed in advance

• Published in: Contemporary clinical trials Vol. 30; no. 4; pp. 317 - 320
• Main Authors: Ahn, Chul, Hu, Fan, Skinner, Celette Sugg, Ahn, Daniel
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.07.2009; Elsevier
• Subjects: Binary outcomes; Biological and medical sciences; Cardiovascular; Clinical trial. Drug monitoring; Cluster Analysis; Computerized, statistical medical data processing and models in biomedicine; Data Interpretation, Statistical; Epidemiology; General aspects; General pharmacology; Hematology, Oncology and Palliative Medicine; Humans; Intracluster correlation; Medical sciences; Medical statistics; Methodology; Models, Statistical; Pharmacology. Drug treatments; Public health. Hygiene; Public health. Hygiene-occupational medicine; Randomized Controlled Trials as Topic - methods; sample size; Varying cluster size; Intracluster correlation; Varying cluster size; sample size; Binary outcomes; Correlation coefficient; Correlation; Randomization; Statistical analysis; Prognosis; Sample size; Clinical trial; Cluster
• DOI: 10.1016/j.cct.2009.03.007
• ISSN: 1551-7144; 1559-2030

In some cluster randomization trials, the number of clusters cannot exceed a specified maximum value due to cost constraints or other practical reasons. Donner and Klar [Donner A, and Klar N. Design and analysis of cluster randomization trials in health research. Oxford University Press 2000] provided the sample size formula for the number of subjects required per cluster when the number of clusters cannot exceed a specified maximum value. The sample size formula of Donner and Klar assumes that the number of subjects is the same in each cluster. In practical situations, the number of subjects may be different among clusters. We conducted simulation studies to investigate the effect of the cluster size variability ( κ) and the intracluster correlation coefficient ( ρ) on the power of the study in which the number of available clusters is fixed in advance. For the balanced case ( κ = 1.0), i.e., equal cluster size among clusters, the sample size formula yielded empirical powers close to the nominal level even when the number of available clusters per group ( k ⁎) is as small as 10. The sample size formula yielded empirical powers close to the nominal level when the number of available clusters per group ( k ⁎) is at least 20 and the imbalance parameter ( κ) is at least 0.8. Empirical powers were close to the nominal level when ( ρ ≤ 0.02, κ ≥ 0.8, and k ⁎ = 10) or ( ρ ≤ 0.02, κ = 0.8, and k ⁎ = 20).