Sequence number (SEQ) is a unique number assigned to each discharge. SEQ does not match the sequence number SEQ_SID. Beginning in the 1998 data, the data element KEY is used instead of SEQ on all HCUP databases.

Beginning in 1994:

The Nationwide Inpatient Sample is sorted by SEQ. SEQ is only included in the Nationwide Inpatient Sample, not the State Inpatient Databases.

SEQ_SID is included in both the Nationwide Inpatient Sample and the State Inpatient Databases. SEQ_SID is identical for discharges present in both the Nationwide Inpatient Sample and State Inpatient Databases. The State Inpatient Databases are sorted by SEQ_SID.

From 1988-1993:

Both the Nationwide Inpatient Sample and the State Inpatient Databases are sorted by SEQ. SEQ is identical for discharges present in both the HCUP Nationwide Inpatient Sample and State Inpatient Databases.

SEQ_SID is not included in either the HCUP Nationwide Inpatient Sample or the State Inpatient Databases.