The National Hospital Discharge Survey and Nationwide Inpatient Sample: The Databases Used Affect Results in THA Research

Abstract

Background The National Hospital Discharge Survey (NHDS) and the Nationwide Inpatient Sample (NIS) collect sample data and publish annual estimates of inpatient care in the United States, and both are commonly used in orthopaedic research. However, there are important differences between the databases, and because of these differences, asking these two databases the same question may result in different answers. The degree to which this is true for arthroplasty-related research has, to our knowledge, not been characterized. Question/purposes We tested the following null hypotheses: (1) there are no differences between the NHDS and NIS in patient characteristics, comorbidities, and adverse events in patients with hip osteoarthritis treated with THA, and (2) there are no differences between databases in factors associated with inpatient mortality, adverse events, and length of hospital stay after THA. Methods The NHDS and NIS databases use different methods of data collection and weighting to provide data representative of all nonfederal hospital discharges in the United States. In 2006 the NHDS database contained 203,149 patients with hip arthritis treated with hip arthroplasty, and the NIS database included 193,879 patients. Multivariable analyses for factors associated with inpatient mortality, adverse events, and days of care were constructed for each database. Results We found that 26 of 42 of the factors in demographics, comorbidities, and adverse events after THA in the NIS and NHDS databases differed more than 10%. Age and days of care were associated with inpatient mortality with the NHDS and the NIS although the effect rates differ more than 10%. The NIS identified seven other factors not identified by the NHDS: wound complications, congestive heart failure, new mental disorder, chronic pulmonary disease, dementia, geographic region Northeast, acute postoperative anemia, and sex, that were associated with inpatient mortality even after controlling for potentially confounding variables. For inpatient adverse events, atrial fibrillation, osteoporosis, and female sex were associated with the NHDS and the NIS although the effect rates differ One of the authors (SB) certifies that he or she has received, during the study period, funding from VU University Amsterdam, faculty fund. One of the authors (AGJB) certifies that he or she has received, during the study period, funding from an AnnaFonds Travel grant (Dutch Orthopaedic travel grant) (less than USD 10,000), VSB-fonds, a nonmedical study grant (USD 10,000 to USD 100,000) and Prins Bernhard Cultuurfonds, Banning-de Jong fonds, a nonmedical study grant for excellent Dutch students USD 10,000 to USD 100,000). One of the authors (DR) certifies that he or she, or a member of his or her immediate family, has received or may receive payments or benefits, during the study period, an amount of USD (less than USD 10,000), from Wright Medical Technologies, Inc (Arlington, TN, USA), Biomet, Inc (Warsaw, IN, USA), Skeletal Dynamics Inc (Miami, FL, USA), AO Nor...

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