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Selecting the optimal longitudinal cluster randomized design with a continuous outcome: Parallel-arm, crossover, or
Jingxia Liu1,2, Fan Li3,4, Siobhan Sutcliffe1
1Division of Public Health Sciences, Department of Surgery, Washington University School of Medicine, St Louis, MO, USA.
Statistical Methods in Medical Research
|August 11, 2025
Summary
This study identifies the optimal design for longitudinal cluster randomized trials. Optimal closed-cohort cluster randomized crossover trials offer the best balance of low cost and high power across various designs.
Area of Science:
- Biostatistics
- Clinical Trial Design
- Epidemiology
Background:
- Longitudinal cluster randomized trials (CRTs) are essential for evaluating interventions in group-level studies.
- Optimal designs (ODs) for parallel-arm, CRXO, and SW-CRT designs have been studied independently.
- A unified understanding of global ODs across different longitudinal designs is lacking.
Purpose of the Study:
- To compare optimal design features across complete longitudinal cluster randomized trial designs.
- To identify a global optimal design that minimizes cost for a desired power or maximizes power within a fixed budget.
- To compare six specific longitudinal cluster randomized trial designs.
Main Methods:
- Utilized a cost-efficiency framework based on generalized estimating equations (GEEs).
- Developed algorithms to determine the optimal number of clusters and participants per cluster per period for each design.
- Employed a block exchangeable correlation structure for equitable comparisons.
Main Results:
- Optimal designs were determined based on lowest cost for desired power or highest power for a fixed budget.
- Suggested using L=T-1 treatment sequences for optimal closed-cohort and repeated cross-sectional SW-CRTs to minimize cost.
- Optimal closed-cohort CRXO trials emerged as global ODs, achieving both minimal cost and maximal power.
Conclusions:
- Optimal closed-cohort cluster randomized crossover (CRXO) trials represent a global optimal design for longitudinal studies.
- This design provides the most cost-effective and powerful approach compared to other evaluated longitudinal CRT designs.
- Findings offer guidance for selecting the most efficient design in cluster randomized trials.
Keywords:
Block exchangeable correlation structurecluster randomized crossoveroptimal design under a budgetary constraintparallel-arm longitudinal cluster randomized trialstepped wedge cluster randomized trialsMore Related Videos
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