By default, SAS Visual Statistics handles missing values by dropping all observations
                  that contain a 
missing value in any 
assigned role variable. However, the Linear Regression, Logistic Regression, and Generalized Linear
                  Model models provide the 
Informative missingness property. In some cases, the fact that an 
observation contains a missing value provides relevant modeling information. Selecting this property
                  explicitly models missing values of variables as a separate variable. For measure
                  variables, missing values are 
imputed with the observed mean, and an 
indicator variable is created to denote missingness. For category variables, missing values are considered
                  a distinct level.