N_HOSP_F contains the number of frame state hospitals in the strata (STRATUM). Beginning in the 1998 NIS, this data element is not included in the data set.

This variable is missing for zero-weight hospitals (see the File Composition for the Nationwide Inpatient Sample for a definition of zero-weight hospitals). Zero-weight hospitals are included in the 1988-1992 data for NIS, Release 1. Because relatively few hospitals were affected and the complexity of including these hospitals entailed considerable processing burden and costs, no zero-weight hospitals are included in the NIS after 1992.