For SAS numeric variables, the SAS DSC writes a period (.) to indicate a missing value. For SAS character variables, the SAS DSC writes a space to indicate a missing value.

For all Metadata Model (MDM) variable types, the SAS DSC writes a missing value if the response to the MDM variable is NULL.

The SAS DSC also writes missing values in the following situations:

When the SAS DSC writes missing Values: The SAS DSC writes the missing value to the SAS variable if the MDM category that corresponds to the categorical response has the flUser flag set. Typically, the flUser flag is set for special categories such as Don't Know.

When the SAS DSC writes Missing Values: The SAS DSC writes the missing value to all the SAS variables in the set if the MDM category that corresponds to the categorical response has the flUser flag set.

The SAS DSC also writes the missing value to unused SAS variables in the set when a response (that does not correspond to a special category) contains less categories than there are variables in the set.

When the SAS DSC writes Missing Values: The SAS DSC writes the missing value to all the SAS variables in the set if the MDM category that corresponds to the categorical response has the flUser flag set.

When the SAS DSC writes Missing Values: For non-categorical MDM variables that have a codes list, the SAS DSC writes the missing value to the SAS variable that corresponds to the MDM variable if the coded response corresponds to an MDM category (in the codes list) that has the flUser flag set.

In the same situation, the SAS DSC might also write the missing value to the one or more SAS variables that correspond to the MDM variable's codes list. For more information, see one of the three entries above, depending on how the SAS DSC has mapped the codes list to SAS variables. (For more information about how the SAS DSC maps codes lists, see "Variables that have Codes Lists" in Variable definitions.)