The ICPHREG Procedure

Observations that contain a missing value for both the left boundary value and the right boundary value in the response are not used in the analysis. If a FREQ variable value is missing or 0, the observation is not used. If any explanatory variable that is specified in the MODEL statement has a missing value, that observation is not used in the model fitting. Predicted values are computed for all observations that have no missing explanatory variable values.