DOES CASE-MIX MATTER FOR SUBSTANCE-ABUSE TREATMENT - A COMPARISON OF OBSERVED AND CASE MIX-ADJUSTED READMISSION RATES FOR INPATIENT SUBSTANCE-ABUSE TREATMENT IN THE DEPARTMENT-OF-VETERANS-AFFAIRS

Objective. To develop a case mix model for inpatient substance abuse t reatment to assess the effect of case mix on readmission across Vetera ns Affairs Medical Centers (VAMCs). Data Sources/Study Setting. The co mputerized patient records from the 116 VAMCs with inpatient substance abuse treatment programs between 1987 and 1992. Study Design. Logisti c regression was used on patient data to model the effect of demograph ic, psychiatric, medical, and substance abuse factors on readmission t o VAMCs for substance abuse treatment within six months of discharge. The model predictions were aggregated for each VAMC to produce an expe cted number of readmissions. The observed number of readmissions for e ach VAMC was divided by its expected number to create a measure of fac ility performance. Confidence intervals and rankings were used to exam ine how case mix adjustment changed relative performance among VAMCs. Data Collection/Extraction Methods. Ward where care was provided and I CD-9-CM diagnosis codes were used to identify patients receiving treat ment for substance abuse (N = 313,886). Principal Findings. The case m ix model explains 36 percent of the observed facility level variation in readmission. Over half of the VAMCs had numbers of readmissions tha t were significantly different than expected. There were also noticeab le differences between the rankings based on actual and case mix-adjus ted readmissions. Conclusions. Secondary data can be used to build a r easonably stable case mix model for substance abuse treatment that wil l identify meaningful variation across facilities. Further, case mix h as a large effect on facility level readmission rates for substance ab use treatment. Uncontrolled facility comparisons can be misleading. Ca se mix models are potentially useful for quality assurance efforts.