Objective: To determine the importance of case-mix adjustment in interpreting differences in rates of pressure ulcer development in Department of Veterans Affairs long-term care facilities.
Design: A sample assembled from the Patient Assessment File, a Veterans Affairs administrative database, was used to derive predictors of pressure ulcer development; the resulting model was validated in a separate sample. Facility-level rates of pressure ulcer development, both unadjusted and adjusted for case mix using the predictive model, were compared.
Setting: Department of Veterans Affairs long-term care facilities.
Patients: The derivation sample consisted of 31 150 intermediate medicine and nursing home residents who were initially free of pressure ulcers and were institutionalized between October 1991 and April 1993. The validation sample consisted of 17 946 residents institutionalized from April 1993 to October 1993.
Measurement: Development of a stage 2 or greater pressure ulcer.
Results: 11 factors predicted pressure ulcer development. Validated performance properties of the resulting model were good. Model-predicted rates of pressure ulcer development at individual long-term care facilities varied from 1.9% to 6.3%, and observed rates ranged from 0% to 10.9%. Case-mix-adjusted rates and ranks of facilities differed considerably from unadjusted ratings. For example, among five facilities that were identified as high outliers on the basis of unadjusted rates, two remained as outliers after adjustment for case mix.
Conclusions: Long-term care facilities differ in case mix. Adjustments for case mix result in different judgments about facility performance and should be used when facility incidence rates are compared.