The development of software for fitting linear mixed models was propelled by advances

in statistical methodology and computing power in the late 20th century. These developments,

while providing applied researchers with new tools, have produced a sometimes

confusing array of software choices. At the same time, parallel development of the methodology

in different fields has resulted in different names for these models, including

mixed models, multilevel models, and hierarchical linear models. This book provides a

reference on the use of procedures for fitting linear mixed models available in five popular

statistical software packages (SAS, SPSS, Stata, R/S-plus, and HLM). The intended audience

includes applied statisticians and researchers who want a basic introduction to the

topic and an easy-to-navigate software reference.

 This book is intended to be a reference for practicing statisticians and applied researchers, and could be used in an

advanced undergraduate or introductory graduate course on linear models.

Given the ongoing development and rapid improvements in software for fitting linear

mixed models, the specific syntax and available options will likely change as newer

versions of the software are released. The most up-to-date versions of selected portions

of the syntax associated with the examples in this book, in addition to many of the data

sets used in the examples, are available at the following Web site: