O'Reilly logo

An Introduction to SAS University Edition by Ron Cody

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

Chapter 16: Working with Multiple Observations per Subject

Introduction

Useful Tools for Working with Longitudinal Data

Describing First. and Last. Variables

Computing Visit-to-Visit Differences

Computing Differences Between the First and Last Visits

Counting the Number of Visits for Each Patient

Conclusion

Problems

Introduction

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 ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required