Setting the boundaries for economic evaluation:Investigating time horizon and family effects in the case of postnatal depression

Objectives This study investigates the impact of varying the boundaries of economic evaluation: time horizon and inclusion of family effects. The context is postnatal mental health, where although advocates for investment often include longer-term and family problems in describing the burden of postnatal depression, economic evaluations are usually limited to mothers’ effects with a relatively short time horizon. This discrepancy may lead to suboptimal allocation of healthcare resources. Methods The question of whether such boundary extensions could make a difference to decision-making is explored using decision analytic models, populated with data from the literature, to estimate the cost-effectiveness of a hypothetical preventive intervention under alternate boundary-setting approaches. Results The results suggest that broader boundaries, particularly extension of the time horizon, could make substantial differences to estimated cost-effectiveness. Inclusion of family effects without extension of the time horizon had little impact, but where a longer time horizon was used, family effects could make a significant difference to the conclusions drawn from cost-effectiveness analysis. Conclusions Considerations in applying broader boundaries include the substantial resource requirements for evaluation, potential equity implications, relevance to decision-makers, methods for inclusion, and the interpretation and use of such results in decision-making. However, this context underscores the importance of considering not only caregiving but also family health effects, and illustrates the need for consistency between the arguments presented to decision-makers and the analytical approach taken in economic evaluation.