PROC REG constructs only one crossproducts
matrix for the variables in all regressions.
If any variable needed for any regression is missing,
the observation is excluded from all estimates.
If you include variables with missing values in the VAR statement,
the corresponding observations are excluded from all analyses,
even if you never include the variables in a model.
PROC REG assumes that you may want to include
these variables after the first RUN statement
and deletes observations with missing values.
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.