Sample size and power calculations based on generalized linear mixed models with correlated binary outcomes

Comput Methods Programs Biomed. 2008 Aug;91(2):122-7. doi: 10.1016/j.cmpb.2008.03.001. Epub 2008 May 6.


The generalized linear mixed model (GLIMMIX) provides a powerful technique to model correlated outcomes with different types of distributions. The model can now be easily implemented with SAS PROC GLIMMIX in version 9.1. For binary outcomes, linearization methods of penalized quasi-likelihood (PQL) or marginal quasi-likelihood (MQL) provide relatively accurate variance estimates for fixed effects. Using GLIMMIX based on these linearization methods, we derived formulas for power and sample size calculations for longitudinal designs with attrition over time. We found that the power and sample size estimates depend on the within-subject correlation and the size of random effects. In this article, we present tables of minimum sample sizes commonly used to test hypotheses for longitudinal studies. A simulation study was used to compare the results. We also provide a Web link to the SAS macro that we developed to compute power and sample sizes for correlated binary outcomes.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Algorithms*
  • Biometry / methods*
  • Computer Simulation
  • Data Interpretation, Statistical
  • Linear Models*
  • Logistic Models*
  • Models, Biological*
  • Outcome Assessment, Health Care / methods*
  • Sample Size*