Chapter 16: Working with Multiple Observations per Subject
Because SAS processes one observation at a time, you need special programming tools when you want to analyze data where there are multiple observations per subject or any other grouping variable. For example, suppose you have a data set in which each observation represents a patient visit to a clinic. You record the patient ID, the date of the visit, and some health-related values. Some common programming tasks would include computing differences in values from visit to visit or differences between the first visit and the last visit for each patient. This chapter describes methods for solving problems of this type.
Useful Tools for Working with Longitudinal Data
Three useful ...