National Hospital Discharge and Ambulatory Surgery Data
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National Survey of Ambulatory Surgery (NSAS) Data Collection and Processing

Data collection for the National Survey of Ambulatory Surgery (NSAS) consisted entirely of manual data collection. Sample selection and abstraction of information from medical records were performed at the facilities. Facility staff did the sampling in about 44 percent of the facilities that participated in the 1996 survey. Facility staff abstracted the data in approximately two-thirds of the participating facilities. In the remaining facilities, the work was performed by personnel of the U.S. Bureau of the Census on behalf of NCHS.

The medical abstract form contains items relating to the personal characteristics of the patients such as age, sex, race, and ethnicity. There are administrative items such as date of procedure, disposition and expected sources of payment. The medical information about patients includes up to seven diagnoses and six procedures, which are coded according to the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM).

All medical coding and keying operations were subject to quality control procedures. These procedures utilized a two-way 10 percent independent verification procedure in which abstracts were independently recoded by a second coder, with discrepancies resolved by the chief coder. Error rates were calculated for nonmedical and medical information based on discrepancies in codes between the independent and the original coder. When error rates exceeded set standards for either nonmedical or medical coding, the medical or nonmedical information was recoded for the entire batch of abstracts and again subjected to quality control procedures.

After medical coding and keying were completed, extensive computer editing was conducted to assure that all responses were accurate, consistent, logical and complete. When necessary, records were reviewed manually to resolve inconsistencies. Missing age and sex data were imputed using a hot deck procedure. A detailed description of the NSAS data collection procedures is included in "The Plan and Operation of the National Survey of Ambulatory Surgery," Vital and Health Statistics Series 1, Number 37.
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