Introduction

Many data sets contain missing values. There are several ways in which missing values can enter a SAS data set. First of all, the raw data value may be missing, either intentionally or accidentally. Next, an invalid value can cause a missing value to be created. For example, reading a character value with a numeric informat will generate a missing value. Invalid dates are another common cause of SAS generated missing values. Finally, many operations, such as assignment statements, can create missing values. This chapter investigates ways to detect and count missing values for numeric and character variables.