TY - JOUR
T1 - Effect of imbalance and intracluster correlation coefficient in cluster randomization trials with binary outcomes when the available number of clusters is fixed in advance
AU - Ahn, Chul
AU - Hu, Fan
AU - Skinner, Celette Sugg
AU - Ahn, Daniel
N1 - Funding Information:
This work was supported in part by NIH grants UL1 RR024982, R01 CA122330, and R01 HL087768.
PY - 2009/7
Y1 - 2009/7
N2 - 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).
AB - 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).
KW - Binary outcomes
KW - Intracluster correlation
KW - Varying cluster size
KW - sample size
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U2 - 10.1016/j.cct.2009.03.007
DO - 10.1016/j.cct.2009.03.007
M3 - Article
C2 - 19348965
AN - SCOPUS:67349122767
SN - 1551-7144
VL - 30
SP - 317
EP - 320
JO - Contemporary Clinical Trials
JF - Contemporary Clinical Trials
IS - 4
ER -