Value of the time trade off method for measuring utilities in patients with rheumatoid arthritis

OBJECTIVE To assess the feasibility, reliability, and validity of the time trade off (TTO) in patients with rheumatoid arthritis (RA). METHODS The TTO was applied in 194 patients with RA with increasing difficulty in performing activities of daily living. The test-retest reliability was determined in 35 of these patients and was calculated by the intraclass correlation coefficient (ICC). Construct validity was evaluated with the following sets of variables: measures of utility (rating scale), quality of life (RAND 36 item Health Status Survey (RAND-36) and RAQoL), functional status (Health Assessment Questionnaire, grip strength, and walk test), and disease activity (doctor's global assessment, disease activity score, pain, and morning stiffness). RESULTS Ten patients (5%) did not complete the TTO. The median value of the TTO was 0.77 (range 0.03–1.0). The test-retest ICC of the TTO was 0.85 (p