Indirect cost assessment in patients with rheumatoid arthritis (RA): comparison of data from the health economic patient questionnaire HEQ-RA and insurance claims data. - Merkesdal,S.; Ruof,J.; Hülsemann,J.L.; Mittendorf,T.; Handelmann,S.; Mau,W.; Zeidler,H. (Arthritis Rheum, 2005)