Patterns of responses in time trade-off studies: a latent class analysis of health states worse than dead.

Abstract

Aim: The study was to characterize participant responses in a time trade-off (TTO) task involving states worse than dead (WTD) to determine patterns of congruence and incongruence.

Methods: The online TTO task involved 4 hypothetical health states describing a rare paediatric condition. Participants completed the task from a parental perspective with a 10-year time horizon. Mean health utilities were derived for the health states (HS). Congruence patterns were defined a priori as "perfect", i.e. completely logical sequence of health state utilities, "incongruent", reversal of the most and least severe HS utilities, and "mixed" congruence. A multinomial regression and latent class analysis (LCA) were applied to elucidate congruence patterns.

Results: A total of 322 participants completed the TTO (49% females; average age 43 years). Perfect congruence response patterns were observed in only 11.5% (37) participants; 99 participants (30.8%) had incongruent response patterns and 186 (57.8%) a mixture. Two (most severe) HS were rated WTD by the "mixed", but only one HS was rated WTD by the "perfect" congruence group, who rated the other 3 HS better than dead. The multinomial regression identified age and gender as potential factors influencing congruence patterns; the most impactful factor was the number of stated rated WTD. The LCA was not able to identify a single class of perfectly congruent responders.

Limitations: This online TTO did not allow further exploration of individual choices through post-task participant interviews.

Conclusions: Facets of TTO tasks such as states WTD may introduce an additional cognitive burden on participants and impact on congruence. However, incongruence was observed even within ostensibly perfectly congruent responses; conversely incongruent response patterns showed some internal coherence. Removing the latter in favour of the former may therefore also introduce bias. A balance may need to be struck between sacrificing perfect congruence and the inclusion of some incongruence to achieve greater representativeness of health state utilities.