GETTING THE COST RIGHT IN COST-EFFECTIVENESS ANALYSES

Objective: The authors examined different ways of measuring unit costs and how methodological assumptions can affect the magnitude of cost e stimates and the ratio of treatment costs in comparative studies of me ntal health interventions. Four methodological choices may bias cost e stimates: study perspective, definition of the opportunity cost of res ources, cost allocation rules, and measurement of service units. Metho d: Unit costs for outpatient services, individual therapy, and group t herapy were calculated under different assumptions for a single commun ity mental health center (CMHC). Using hypothetical service utilizatio n profiles, the authors used the unit costs to calculate the costs of mental health treatments provided by two programs of the CMHC. Results : The unit costs for an hour of outpatient services ranged from $108 t o $538. The unit costs for an hour of therapy varied by 156%; unit cos ts were lowest if the management perspective was assumed and highest i f the economist perspective was assumed. The ratio of the outpatient c osts in the two treatment programs ranged from 0.6 to 1.8. Conclusions : The potential errors introduced by methodological choices can bias c ost-effectiveness findings based on randomized control trials. These e rrors go undetected because crucial methodological information is not reported.