Productivity costs among patients with rheumatoid arthritis: the influence of methods and sources to value loss of productivity.

Objective: To assess productivity costs incurred by rheumatoid arthritis, comprising paid as well as household productivity costs, from a societal perspective, using different methods.
Methods: A questionnaire on productivity, including items of the Health and Labour Questionnaire, was completed by 576 patients with rheumatoid arthritis (mean disease duration seven years). The friction cost (FC) method using the gross national wage per hour was applied to estimate paid productivity, and the market equivalent was used to value loss of household productivity. Sensitivity analyses to estimate paid productivity costs among patients of working age included the human capital (HC) method and an alternative source, namely the "added value", to value loss of paid productivity.
Results: In the total study population, mean (SD) annual costs from loss of paid productivity according to the FC method were estimated to be 278 (1,559) and mean annual household productivity costs were 2,045 (3,882). When using the HC method, mean annual costs increased to an average of 4,434 (9,957). When using the added value of production, average FC costs increased from 455 to 540 among patients of working age.
Conclusions: Costs from loss of household productivity in rheumatoid arthritis were seven times higher than costs from loss of paid productivity, assessed by the FC method. The high paid productivity costs when using the HC method reflect the high work disability rate in rheumatoid arthritis. As the method of measuring and source of valuing productivity loss has an important influence on the costs, a consensus to standardise these issues is desirable.