Thirty down, only ten to go?! Awareness and influence of a 10-year time frame in TTO

Abstract

Time trade-off (TTO) exercises typically present respondents with a limited time horizon, for example 10 years, thus implicitly considerably reducing remaining life expectancy for the average respondent. It is unclear how this affects health state valuations. The aim of the study is to investigate how awareness of the reduced life span implied by a 10-year TTO affects health state valuations, using an experimental design. Two Web-based questionnaires (Q1 and Q2) were administered in a sample representative of the Dutch population. Both questionnaires contained three 10-year TTO exercises valuing three distinct health states, specified using the EQ-5D. Q1 used a TTO instruction not explicitly emphasizing the fact that remaining life expectancy was reduced to 10 years, while in Q2 respondents were explicitly made aware of this fact by emphasizing their implied age of death. Respondents answering Q1 were asked retrospectively whether they had been aware of their reduced life span due to the 10-year TTO. In total, 656 respondents completed the questionnaires (Q1: 339 and Q2: 317). The average age of the respondents was 43 years and 51 % of respondents were male. The average numbers of years traded off for the respondents of Q1 were for TTO1 0.443, TTO2 0.552, and TTO3 2.083 years. For the respondents of Q2, these averages were lower, i.e., TTO1 0.401 (p = 0.085 vs. Q1), TTO2: 0.546 (p = 0.036 vs. Q1), and TTO3: 1.467 years (p = 0.000 vs. Q1). Fifty-seven percent of respondents in Q1 confirmed that they were aware of the reduced life span. This spontaneous awareness had a limited and mixed influence on results. The generalized negative binomial regression analysis, explaining the time traded off showed that age, subjective life expectancy, and questionnaire Q2 (vs. Q1) were negatively associated with the years traded off, whereas education and worse health states in the TTO exercise had a significant positive impact on the years traded off. The probit model investigating the impact on the willingness to trade showed that age (-), education (+), subjective life expectancy (-), questionnaire Q2 versus Q1 (-), the interaction between Q2 and male gender (+), and worse health states in the TTO exercise (+) had a significant impact on the willingness to trade. These findings emphasize the importance of expected and implied life expectancy in TTOs.