Estimates from two survey designs: national hospital discharge survey

The methodology for the National Hospital Discharge Survey (NHDS) has been revised in several ways. These revisions, which were implemented for the 1988 NHDS, included adoption of a different hospital sampling frame, changes in the sampling design (in particular the implementation of a three-stage design), increased use of data purchased from abstracting service organizations, and adjustments to the estimation procedures used to derive the national estimates. To investigate the effects of these revisions on the estimates of hospital use from the NHDS, data were collected from January through March of 1988 using both the old and the new survey methods. This study compared estimates based on the old and the new survey methods for a variety of hospital and patient characteristics. Although few estimates were identical across survey methodologies, most of the variations could be attributed to sampling error. Estimates from two different samples of the same population would be expected to vary by chance even if precisely the same methods were used to collect and process the data. Because probability samples were used for the old and new survey methodologies, sampling error could be measured. Approximate relative standard errors were calculated for the estimates using the old and new survey methods. Taking these errors into account, less than 10 percent of the estimates were found to differ across survey methodologies at the 0.05 level of significance. Because a large number of comparisons were made, 5 percent of the estimates could have been found to be significantly different by chance alone. When there were statistically significant differences in nonmedical data, the new methods appeared to produce more accurate estimates than the old methods did. Race was more likely to be reported using the new methods. "New" estimates for hospitals in the West Region and government-owned hospitals were more similar than the corresponding "old" estimates to data from the census of hospitals conducted by the American Hospital Association. The numerous significant differences in estimates for bed size categories between the two survey methodologies reflected the change in the universe and definition of beds for the new survey. Few statistically significant differences were found in the medical data using the old and the new survey methods. Two main differences, in estimates for cataract and alcohol dependence syndrome, may have resulted from problems with the new survey. A measurement error, reporting outpatients to the NHDS, is one possible explanation of the higher estimates for diagnosis of cataract using the new survey methods.(ABSTRACT TRUNCATED AT 400 WORDS)