## Abstract

Stepped wedge cluster trials are an increasingly popular alternative to traditional parallel cluster randomized trials. Such trials often utilize a small number of clusters and numerous time intervals, and these components must be considered when choosing an analysis method. A generalized linear mixed model containing a random intercept and fixed time and intervention covariates is the most common analysis approach. However, the sole use of a random intercept applies a constant intraclass correlation coefficient structure, which is an assumption that is likely to be violated given stepped wedge trials (SWTs) have multiple time intervals. Alternatively, generalized estimating equations (GEE) are robust to the misspecification of the working correlation structure, although it has been shown that small-sample adjustments to standard error estimates and the use of appropriate degrees of freedom are required to maintain the validity of inference when the number of clusters is small. In this article, we show, using an extensive simulation study based on a motivating example and a more general design, the use of GEE can maintain the validity of inference in small-sample SWTs with binary outcomes. Furthermore, we show which combinations of bias corrections to standard error estimates and degrees of freedom work best in terms of attaining nominal type I error rates.

Original language | English |
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Pages (from-to) | 2779-2792 |

Number of pages | 14 |

Journal | Statistics in Medicine |

Volume | 39 |

Issue number | 21 |

DOIs | |

State | Published - Sep 20 2020 |

### Bibliographical note

Publisher Copyright:© 2020 John Wiley & Sons, Ltd.

## Keywords

- degrees of freedom
- empirical standard error
- generalized estimating equations
- group randomized trials
- test size

## ASJC Scopus subject areas

- Epidemiology
- Statistics and Probability