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power swgee: GEE-based power calculations in stepped wedge cluster randomized trials.

John A Gallis1, Xueqi Wang1, Paul J Rathouz2

  • 1Department of Biostatistics, Duke University, Duke Global Health Institute, Durham, NC.

The Stata Journal
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Summary

A new Stata tool simplifies power calculations for stepped wedge cluster randomized trials (SW-CRTs). This calculator uses generalized estimating equations (GEE) for accurate sample size determination in complex trial designs.

Keywords:
generalized estimating equationsgroup randomized trialsmarginal modelspower swgeest0001statistical power

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Area of Science:

  • * Biostatistics
  • * Health Services Research
  • * Social Sciences

Background:

  • * Stepped wedge cluster randomized trials (SW-CRTs) are widely used across various disciplines.
  • * The complex longitudinal and crossover nature of SW-CRTs presents challenges in sample size calculation.
  • * Existing power calculators may not suit the primary analysis methods for SW-CRTs.

Purpose of the Study:

  • * To introduce a novel SW-CRT power calculator integrated into Stata.
  • * To provide a tool that accommodates marginal models, specifically generalized estimating equations (GEE), for SW-CRT analysis.
  • * To support complete cross-sectional and closed-cohort SW-CRT designs.

Main Methods:

  • * Development of a new power calculator command (`power swgee`) within Stata.
  • * Implementation of formulae based on marginal models (GEE) for SW-CRT power calculations.
  • * Inclusion of multilevel correlation structures suitable for SW-CRT designs.

Main Results:

  • * The `power swgee` command offers a new method for powering SW-CRTs using GEE.
  • * The calculator supports both complete cross-sectional and closed-cohort designs.
  • * Illustrative examples demonstrate the practical application of the `power swgee` command.

Conclusions:

  • * The developed Stata tool addresses a critical need for accurate SW-CRT power calculations.
  • * The calculator's use of GEE makes it suitable for a common primary analysis approach.
  • * Future research directions are identified to enhance the calculator's capabilities.