[Conceptual and methodological basics of cost assessments in rheumatology].

Cost-of-illness studies in rheumatic conditions show an enormous variability in reported costs. Reasons are-among others-a lack of standardization with regards to relevant cost domains and the utilization of various insufficiently validated costing sources. A flow scheme is presented which may serve as a systematic basis for a valid costing analysis. The scheme includes: i) Selection of relevant cost domains. A comprehensive matrix of cost domains may be used as a framework. According to the specific aims of any costing study individual domains might be selected. ii) An adequate level of detail has to be determined taking into account factors such as the validity of the data collection and the feasibility. iii) Appropriate objective (i. e. usage of administrative data) or subjective (i. e. patient-derived) data sources have to be identified under consideration of respective strengths and weaknesses. While administrative sources provide a valid access to costing data accessibility and feasibility are important advantages of patient-derived costing procedures. iv) During data collection the potential bias due to protocol-driven costs and the differentiation of disease-related from other health care costs should be considered. v) The data analysis should support a transparent presentation of the costing data both in physical and monetary units. In summary, no 'gold standard' has been established for costing studies yet. However, valid costing approaches might follow the flow scheme presented in this analysis.