Construct Validity and Responsiveness of EQ-5D-3L in Patients With Rheumatic Disease

Inclusion Criteria: * 18 years and older at the time of first included measurement * A diagnosis of RA, polyarthritis, PsA, or AS * Complete registration of responses in the EQ-5D-3L descriptive system or EQ VAS on at least one time point in SRQ * For patients with RA: At least one measurement with Disease Activity Score 28 (DAS28) reported in relation to the same visit as EQ-5D-3L * For patients with polyarthritis: At least one measurement with DAS28 reported in relation to the same visit as EQ-5D-3L * For patients with PsA: At least one measurement with DAS28 or Disease Activity in Psoriatic Arthritis (DAPSA) reported in relation to the same visit as EQ-5D-3L * For patients with AS: At least one measurement with the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) reported in relation to the same visit as EQ-5D-3L For the analyses of construct validity, the latest measurement will be used if the individual patients have multiple complete registrations with EQ-5D-3L and the other required measure. The hypotheses for responsiveness will be tested in patients with newly diagnosed disease (having the diagnosis for ≤12 months), as changes in disease activity are likely to be present in this group. For the analysis of responsiveness, the two first measurements during the first year will be used.