Time Trade-off Utility Assessment with a 10-Year Time Horizon: when Should Alternative Approaches Be Considered?

In recent years, the time trade-off (TTO) method with a 10-year time horizon has been the most frequently used approach for direct health-state utility assessment. It is likely that researchers have favored this method because the National Institute of Health and Clinical Excellence (NICE) Guide to the Methods of Technology Appraisal states a preference for consistency with the EQ-5D, which has a utility scoring algorithm derived using 10-year TTO valuations. Although comparability to previous utility studies is important, there are situations when the 10-year TTO is not optimal. A review of the literature was conducted to identify situations when TTO with a 10-year time horizon may not be the most appropriate method for eliciting health-state utilities. Five challenges to the 10-year TTO method include mild health states, small differences among health states, temporary health states, pediatric health states, and assessment of samples with particular characteristics. In these situations, the 10-year TTO may not yield valid utility scores, detect small but important differences among health states, or accurately represent the clinical condition being studied. Alternative approaches are suggested, including variations of the TTO (e.g., varying the time horizon), other direct utility assessment methods (e.g., standard gamble with or without chaining), measures developed specifically for children, mapping condition-specific health-related quality of life questionnaires to generic preference measures, and condition-specific preference-based measures derived from longer condition-specific questionnaires using Rasch and item-response theory methods. Rather than simply using the most commonly used method, it is recommended that investigators select a utility assessment method based on its relevance and validity for particular clinical contexts and health states. Pilot studies are often helpful in identifying the optimal approach.