Performance of compliance and persistence measures in predicting clinical and economic outcomes using administrative data from German sickness funds.

STUDY

OBJECTIVE

To compare the performance of various compliance and persistence measures in predicting schizophrenia-related hospitalization rates and inpatient costs.

DESIGN

Retrospective, nonrandomized cohort study.

DATA SOURCE: Prescription claims databases from three German sickness funds (public health insurance programs).

PATIENTS: A total of 1484 patients who were hospitalized in 2003 for a schizophrenia-related episode and subsequently received long-term antipsychotic pharmacotherapy.

MEASUREMENTS AND MAIN

RESULTS

Data on age, sex, schizophrenia, prescription drugs, hospitalizations, and inpatient expenditures were collected for each patient from the three German sickness funds. Refill compliance measures based on single-interval availability and multiple-interval availability, as well as refill persistence, were calculated for each patient over 1 year. Ten measurement variables were compared with respect to their performance in predicting disease-related hospitalization and inpatient expenditure, using multivariate logistic regression and gamma regression, respectively. C-statistics were calculated to determine each measure's predictive performance. Likelihood ratio tests showed that inclusion of compliance and persistence measures significantly improved (p<0.05) outcomes prediction in 6 of 10 hospitalization models and in 3 of 10 inpatient cost models compared with a baseline model that included only age, sex, and disease severity covariates. Refill compliance as a continuous variable of drug persistence, including transfer of oversupplies into subsequent periods, performed best in predicting hospitalization (C = 0.669). Availability ratios, capped at 100%, were superior to default availability ratios in predicting hospitalization. Allowing for cross-period carryover improved the discriminatory performance of the persistence models.

CONCLUSION

Refill persistence measures appear sufficiently flexible to account for hospitalizations common in schizophrenia and other psychiatric diseases. A continuous refill persistence measure should be used to assess compliance in psychiatric conditions when working with administrative data.