Cost assessment instrument in rheumatology: evaluation of applied instrument characteristics

We compared the major characteristics of internationally applied cost assessment instruments (CAI) in rheumatic conditions. Fifteen utilization questionnaires were identified and assessed using a structured approach. The forms differed considerably with respect to applied characteristics: length (3-113 items), recall period (between 1 week and 1 year), format (2 interview, 13 self-administered), response categories, cost units (physical vs monetary), and cost domains covered. While all included a gross assessment of outpatient and inpatient costs, the level of disaggregation differed. Only a few CAI included an assessment of other direct disease related costs (e.g., home remodeling or home health care services) and out-of-pocket expenditure. Productivity costs were included in all but 2 CAI. Efforts to further standardize the applied CAI should (1) be based on sound psychometric data, (2) define a required core set of cost domains covered, (3) discriminate between generic and relevant disease related cost components, and (4) examine the feasibility of developing international standards for cost data.