Sample size calculations for studies with correlated observations

Biometrics. 1997 Sep;53(3):937-47.


Correlated data occur frequently in biomedical research. Examples include longitudinal studies, family studies, and ophthalmologic studies. In this paper, we present a method to compute sample sizes and statistical powers for studies involving correlated observations. This is a multivariate extension of the work by Self and Mauritsen (1988, Biometrics 44, 79-86), who derived a sample size and power formula for generalized linear models based on the score statistic. For correlated data, we appeal to a statistic based on the generalized estimating equation method (Liang and Zeger, 1986, Biometrika 73, 13-22). We highlight the additional assumptions needed to deal with correlated data. Some special cases that are commonly seen in practice are discussed, followed by simulation studies.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Biometry / methods
  • Family
  • Humans
  • Longitudinal Studies
  • Models, Statistical*
  • Monte Carlo Method
  • Ophthalmology / methods
  • Regression Analysis
  • Research Design*