This document describes a suite of functions designed to facilitate the analysis of longitudinal data within the S-PLUS statistical programming environment. As the title suggests, these functions take advantage of the object-oriented programming facilities of S-PLUS, meaning that a number of data types have been created specifically for the analysis of longitudinal data, and that many of the `standard' S-PLUS functions have been programmed to behave appropriately with these new data types (see Appendix A for a list of such functions). Thus the number of new function names that need to be remembered has been kept to a minimum, and users already familiar with S-PLUS should be able to operate with the new data types with a minimum of effort.
Although all of the functions described herein are fully documented within S-PLUS with its on-line help system, this document is intended as a somewhat more relaxed introduction to the software. Completeness has sometimes been dispensed with in favour of clarity, however (only the most important optional arguments of each function have been explained, for example) and so for more detailed information the on-line help should be consulted.
We assume a basic familiarity with the S-PLUS system. Any advanced features, however, will be explained (if briefly) when required. The basic reference on S-PLUS is Becker et al. (1988). For information on the statistical features of S-PLUS, consult Chambers & Hastie (1992).
At appropriate points, we shall give brief explanations of the statistical methodology on which the software is based. More detailed explanations can be found in Diggle et al. (1994).