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Intracluster correlation adjustments to maintain power in cluster trials for binary outcomes
Hrishikesh Chakraborty1, Janet Moore, Tyler D Hartwell
1Statistics and Epidemiology, RTI International, Research Triangle Park, North Carolina 27709-2194, USA. hchakraborty@rti.org
Contemporary Clinical Trials
|April 24, 2009
Summary
Sample size calculations for cluster randomized trials depend on intracluster correlation (ICC). Simulation shows ICC estimates are influenced by event rates, variations, and cluster sizes, necessitating sample size adjustments for trial power.
Area of Science:
- Biostatistics
- Clinical Trials Methodology
Background:
- Sample size calculations for cluster randomized trials are crucial for adequate statistical power.
- These calculations are primarily influenced by event rate variability, effect size, average cluster size, and the intracluster correlation (ICC).
- Estimating ICC itself is complex, depending on event rate variability, cluster size, and the number of clusters.
Purpose of the Study:
- To evaluate the impact of various factors on intracluster correlation (ICC) estimates in cluster randomized trials.
- To assess how event rate changes during a trial affect ICC estimates.
- To examine the influence of intervention effects on ICC, confidence intervals, and required sample size.
Main Methods:
- Two simulation exercises were conducted.
- The first simulation investigated the impact of event rates, event rate variations, cluster size, and cluster size variations on ICC estimates and 95% confidence intervals.
- The second simulation examined the effect of intervention/drug effects on ICC, confidence intervals, and sample size across four trial scenarios.
Main Results:
- Intracluster correlation (ICC) estimates are significantly dependent on the event rate, event rate variations, cluster size, cluster size variations, and the number of clusters.
- Adjusting sample size during a trial can help maintain adequate statistical power, especially when intervention effects are considered.
Conclusions:
- Accurate estimation of ICC is vital for reliable sample size calculations in cluster randomized trials.
- The findings highlight the need to consider event rate dynamics and cluster characteristics when planning and conducting these trials.
- Adaptive sample size adjustments may be necessary to ensure sufficient power throughout the trial duration.
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