Construct validity of the interview time trade-off and computer time trade-off in patients with rheumatoid arthritis: a cross-sectional observational pilot study.

Background: The Time Trade-Off (TTO) is a widely used instrument for valuing preference-based health-related quality of life (HRQoL). The TTO reveals preferences for own current health ('utilities') on a scale anchored between death (0) and perfect health (1). Limited information on the external validity of the TTO is available.