Task 1: How to Identify and Recode Missing Data in NHANES I

The first task is to identify missing data and recode it. Here are the steps:

• Identify missing and unavailable values
• Recode unavailable values as missing
• Evaluate extent of missing data

Step 1 Identify missing and unavailable values

In this step, you will use the proc means procedure to check for missing, minimum and maximum values of continuous variables, and the proc freq procedure to look at the frequency distribution of categorical variables in your master analytic dataset. The output from these procedures provides the number and frequency of missing values for each variable listed in the procedure statement. 

WARNING

Typically, proc means is used for continuous variables, and proc freq is used for categorical variables. In the following example, we provide proc means and proc freq procedures on the same set of variables without distinguishing continuous and categorical variables. If you perform a proc freq on a continuous variable with many values, the output could be extensive.