Mixed-Effects Models Jose' C. Pinheiro Biostatistics, Novartis Pharmaceuticals COURSE DESCRIPTION Mixed-effects models provide a powerful tool for analyzing grouped data, because they model flexibly the within-group correlation often present in this type of data. Examples of grouped data include repeated measures, longitudinal data, multilevel data, and some split-plot experiments, being collected in a wide variety of areas. This course describes how to fit and analyze linear and nonlinear mixed-effects models in S, using the NLME library. This is an applied course, with emphasis on real life examples to motivate and illustrate the use of mixed-effects models. OUTLINE 1) Introduction - motivating examples of linear and non-linear mixed-effects models - a sample of S functions and methods for fitting and analyzing mixed-effects models. 2) Grouped data - repeated measures data, longitudinal data, growth curve data - multilevel data - Data structures and Trellis displays for grouped data in S 3) Fitting linear mixed-effects models - the linear mixed-effects (LME) model - using the lme function in S - assessing the adequacy of an LME fit - confidence intervals, hypothesis tests, and predictions - fitting LME models to multilevel data 4) Extending the basic LME model - modeling the random effects covariance structure - variance functions to model unequal within-group variances - serial and spatial within-group correlation structures - an extended linear model with no random effects: the gls function 5) Fitting nonlinear mixed-effects models - brief review of nonlinear regression for independent observations - nonlinear mixed-effects (NLME) models for grouped data - the nlme function in S - assessing the adequacy of an NLME fit - confidence intervals, hypothesis tests, and predictions