Title:
Do productivity costs matter?: the impact of including productivity costs on the incremental costs of interventions targeted at depressive disorders.

Abstract:
When guidelines for health economic evaluations prescribe that a societal perspective should be adopted, productivity costs should be included. However, previous research suggests that, in practice, productivity costs are often neglected. This may considerably bias the results of cost-effectiveness studies, particularly those regarding treatments targeted at diseases with a high incidence rate in the working population, such as depressive disorders.
This study aimed to, first, investigate whether economic evaluations of treatments for depressive disorders include productivity costs and, if so, how. Second, to investigate how the inclusion or exclusion of productivity costs affects incremental costs.
A systematic literature review was performed. Included articles were reviewed to determine (i) whether productivity costs had been included and (ii) whether the studies adhered to national health economic guidelines about the inclusion or exclusion of these costs. For those studies that did include productivity costs, we calculated what proportion of total costs were productivity costs. Subsequently, the incremental costs, excluding productivity costs, were calculated and compared with the incremental costs presented in the original article, to analyse the impact of productivity costs on final results. Regression analyses were used to investigate the relationship between the level of productivity costs and the type of depressive disorder, the type of treatment and study characteristics such as time horizon used and productivity cost valuation method.
A total of 81 unique economic evaluations of treatments for adults with depressive disorders were identified, 24 of which included productivity costs in the numerator and one in the denominator. Approximately 69% of the economic evaluations ignored productivity costs. Two-thirds of the studies complied with national guidelines regarding the inclusion of productivity costs. For the studies that included productivity costs, these costs reflected an average of 60% of total costs per treatment arm. The inclusion or exclusion of productivity costs substantially affected incremental costs in a number of studies. Regression analyses showed that the level of productivity costs was significantly associated with study characteristics such as average age, the methods of data collection regarding work time lost, the values attached to lost work time, the type of depressive disorder, the type of treatment provided and the level of direct costs.
Studies that do not include productivity costs may, in many cases, poorly reflect full societal costs (or savings) of an intervention. Furthermore, when comparing total costs reported in studies that include productivity costs, it should be noted that study characteristics such as the methods used to assess productivity costs may affect their level.