Pharmaceutical Statistics Using SAS

12.1. Introduction

In a longitudinal clinical trial, each unit is measured on several occasions. It is not unusual in practice for some sequences of measurements to terminate early for reasons outside the control of the investigator. Any unit so affected is called a dropout. It might therefore be necessary to accommodate the dropout in the modeling process.

When referring to the missing-value (or non-response) process we will use the terminology of Little and Rubin (1987, Chapter 6). A non-response process is said to be missing completely at random (MCAR) if the missingness is independent of both unobserved and observed data. A process is said to be missing at random (MAR) if, conditional on the observed data, the missingness is independent ...