On the evaluation of drug benefits policy changes with longitudinal claimsdata: the policy maker's versus the clinician's perspective

Cost containment in pharmaceutical-benefit plans are often controversially debated for their potential of unintended consequences on health and overal l expenditures. Thorough evaluations are needed but hypotheses and design c onsiderations are complex. Our objective is to provide a structured framewo rk for the evaluation of drug-benefit changes using longitudinal claims dat a. Differential cost sharing (DCS) will serve as a recent example, Benefit- plan managers are mainly interested in the overall performance of their pla n. In a policy model, any observed policy-related effects may be compared w ith what would have happened had the intervention not been implemented by e xtrapolating the pre-policy trend from the same patients. These estimates w ill reflect the global consequences of the policy maker's decision. However , such estimates represent summary effects of benefits and harms, separatel y identifiable in those complying with the intended policy and those not co mplying. Results from a policy model apply only to a specific policy implem entation and tend to underestimate effects when non-compliance is high. Cli nical-decision makers and patients, by contrast, are interested in the cons equences of patients' actual compliance to the policy. A clinical model ass esses the effects of DCS depending on the actual treatment in contrast to t he treatment intended by the policy. However, this model must sometimes mak e, unprovable assumptions about the appropriate control of selection factor s. In conclusion, both policy and clinical models should be tested with a c lear understanding of their perspectives, hypotheses, and interpretations, using quasi-experimental time-series designs to evaluate the effects of dru g cost-containment policies. (C) 2001 Elsevier Science Ireland Ltd. All rig hts reserved.