Regression for longitudinal data: A bridge from least squares regression

Longitudinal studies play a prominent role in biomedical and sociological research. Generalized estimating equations (GEE) provide a regression methodology to analyze the correlated data that often result from a longitudinal study. Many applied researchers are attracted to the informative and valid analyses GEE provides but cannot clear the hurdle of understanding the literature. This article places GEE in more familiar territory by building a link from the well-known least squares regression methodology.