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National Survey of Ambulatory Surgery (NSAS)

Database Name: National Survey of Ambulatory Surgery (NSAS)

Description/Data source

Survey-based data source sponsored by the National Center for Health Statistics (the primary agency of the Centers for Disease Control and Prevention monitoring health statistics).

Overview of data contents

Most recent dataset includes data from approximately 52,000 ambulatory surgery encounters obtained from 142 hospital-based and 295 freestanding ambulatory surgery centers (74.4% unweighted response rate) using a multi-stage probability design. Data are weighted to create national estimates of ambulatory surgery utilization. Public use file contains variables which include basic patient demographics, source of payment, diagnostic and procedural codes, information about type of anesthetics, surgical times, post anesthesia care unit times, and immediate postoperative complications. Restricted use NCHS data (NCHS Data Research Center) contains patient demographic variables including geographic region, urban/rural setting, and patient race/ethnicity.

Patient ages included

All ages of patients who undergo ambulatory surgery.


Information obtained from hospital-based and freestanding ambulatory surgery centers.

Date range available

Data available for 1994-1996, and for 2006. Data is cross-sectional whereas patient information cannot be followed over time; longitudinal comparisons between the two time periods of data may be broadly made for trends in procedural rates of other ambulatory surgical characteristics. The NSAS is not currently active; however information about ambulatory surgical visits may be included in the future as a function of the National Hospital Ambulatory Medical Care Survey (NHAMCS).

Relevant Work

Example publications

Boss Emily F. Marsteller Jill A. Simon Allen E. Outpatient tonsillectomy in children: demographic and geographic variation in the United State, 2006. Comment in: J Pediatr. 2012 May;160(5):716-8; Journal of Pediatrics. 160(5):814-9, 2012 May.

Mahboubi H. Verma SP. Ambulatory laryngopharyngeal surgery: evaluation of the national survey of ambulatory surgery. JAMA Otolaryngology-Head & Neck Surgery. 139(1):28-31, 2013 Jan.


Cost estimate(s)

Public use file available at no cost.

Contact/website information


Ease of use

After downloaded, dataset user-friendly for researchers versed in appropriate use of statistical software. NCHS staff helpful in accommodating users.

Data analysis

Data is weighted to produce estimates. Publication of estimates is based on the relative standard error of the estimate and the number of sample records on which the estimate is based (the sample size). Estimates are not presented in NCHS reports unless a reasonable assumption regarding the probability distribution of the sampling error is possible. If the sample size is 60 or more and the relative standard error is less than 30 percent, the estimate is reported.


Sole national study of ambulatory surgical care in the US. Survey sampling designed to represent national surgical utilization (as opposed to other surgical databases which represent convenience samples of participating facilities).


Most recent data is from 2006 which may not reflect current trends in healthcare administration and policy. Only assesses patients who undergo surgery, therefore need for surgery, magnitude of symptoms, as well as diagnostic and referral criteria for treatment cannot be assessed. High missing rates of race and ethnicity variables; socioeconomic variables limited (no information on household income or poverty level). Many otolaryngological procedures represent only a portion of ambulatory surgery and therefore have low un-weighted sample sizes, reducing statistical reliability for meaningful comparisons.