title: Validation of case-mix measures derived from self-reports of diagnoses and health.
abstract: Self-reported chronic diseases and health status are associated with resource use. However, few data exist regarding their ability to predict mortality or hospitalizations. We sought to determine whether self-reported chronic medical conditions and the SF-36 could be used individually or in combination to assess co-morbidity in the outpatient setting. The study was designed as a prospective cohort study. Patients were enrolled in the primary care clinics at seven Veterans Affairs (VA) medical centers participating in the Ambulatory Care Quality Improvement Project (ACQUIP). 10,947 patients, > or = 50 years of age, enrolled in general internal medicine clinics who returned both a baseline health inventory checklist and the baseline SF-36 who were followed for a mean of 722.5 (+/-84.3) days. The primary outcome was all-cause mortality, with a secondary outcome of hospitalization within the VA system. Using a Cox proportional hazards model in a development set of 5,469 patients, a co-morbidity index [Seattle Index of Co-morbidity (SIC)] was constructed using information about age, smoking status and seven of 25 self-reported medical conditions that were associated with increased mortality. In the validation set of 5,478 patients, the SIC was predictive of both mortality and hospitalizations within the VA system. A separate model was constructed in which only age and the PCS and MCS scores of the SF-36 were entered to predict mortality. The SF-36 component scores and the SIC had comparable discriminatory ability (AUC for discrimination of death within 2 y 0.71 for both models). When combined, the SIC and SF-36 together had improved discrimination for mortality (AUC = 0.74, p-value for difference in AUC < 0.005). A new outpatient co-morbidity score developed using self-identified chronic medical conditions on a baseline health inventory checklist was predictive of 2-y mortality and hospitalization within the VA system in general internal medicine patients.
authors.affiliation: Health Services Research and Development Center of Excellence, VA Puget Sound Health Care System, Seattle, WA 98108-1597, USA. vfan@u.washington.edu
authors.forename: Vincent S
authors.initials: VS
authors.lastname: Fan
authors.forename: David
authors.initials: D
authors.lastname: Au
authors.forename: Patrick
authors.initials: P
authors.lastname: Heagerty
authors.forename: Richard A
authors.initials: RA
authors.lastname: Deyo
authors.forename: Mary B
authors.initials: MB
authors.lastname: McDonell
authors.forename: Stephan D
authors.initials: SD
authors.lastname: Fihn
mesh_terms: D000368:Aged; D000553:Ambulatory Care; D000704:Analysis of Variance; D002908:Chronic Disease / Q000453:epidemiology*; D015897:Comorbidity; D015986:Confounding Factors, Epidemiologic; D005260:Female; D006304:Health Status; D006760:Hospitalization; D006801:Humans; D008297:Male; D008875:Middle Aged; D009026:Mortality; D011237:Predictive Value of Tests; D016016:Proportional Hazards Models; D011446:Prospective Studies; D011788:Quality of Life; D012372:ROC Curve; D015203:Reproducibility of Results; D012306:Risk; D020379:Risk Adjustment; D011795:Surveys and Questionnaires; D014481:United States; D014861:Washington