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Sample Size Calculations for Studies with Correlated Observations

Guanghan Liu and Kung-Yee Liang
Biometrics
Vol. 53, No. 3 (Sep., 1997), pp. 937-947
DOI: 10.2307/2533554
Stable URL: http://www.jstor.org/stable/2533554
Page Count: 11
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Sample Size Calculations for Studies with Correlated Observations
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Abstract

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.

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