COMPARISON OF DISCRETE DATA METHODS FOR REPEATED MEASURES DATA WITH SMALL SAMPLES

Abstract

Various analytical methods are available to analyze repeated measures data for both continuous and discrete data. In the case of discrete data, most methods are based on the assumption of asymptotic normality, requiring large samples. Naturally, their small sample performance may not match the expectation satisfactorily. Two main methods, the non-linear mixed effects (NLME) model and the generalized estimating equations (GEE) method, are investigated for their small sample performance on repeated binary data. We generated binary data, considering two levels of correlation at rho=0.3 and 0.7, with three cases of repeated measures with T=2, 4, or 6 and sample sizes ranging from 40 to 200. The two analysis methods are applied to each data set in 5000 simulations, and the resulting empirical size and power are compared. We conclude that the GEE performs quite well in small samples with satisfactory empirical size and statistical power and is therefore recommended.