Table 1.

Differences between the NIS and NSQIP

Factor	NIS	NSQIP
Identification of patients	Retrospective, a sample of inpatient discharges	Prospective, a sample of patients identified at participating institutions
Procedure characterization	International classification of disease, 9th revision procedure codes	Current procedure terminology codes
Comorbidity and adverse event data	Reimbursement data in the form of international classification of disease, 9th revision codes	Directed review of medical records by specially trained surgical clinical reviewers, with routine auditing to ensure quality
Time range of data collected	Inpatient only	Inpatient and outpatient up to the 30th postoperative day

NIS = National Inpatient Sample; NSQIP = National Surgical Quality Improvement Program.