More evidence that there are diminishing marginal returns to quality of life gains

A paper by Johnson et al. (2024) conduct a discrete-choice experiment (DCE) in order to quantify patient preferences over treatments for major depressive disorder (MDD). They offered different iterations of severe, moderate and mild depression to test for diminishing marginal utility and path dependence. A deductive latent-class mixed-logit analysis was used to evaluate survey data from 751 respondents with MDD.

Using this approach, they found that:

Consistent with theoretical expectations, we found evidence of diminishing marginal utility,
holding sequence timing constant, as well as evidence of path dependence, holding symptom improvement constant. Our experiment isolated the effects of path dependence from the influence of conventional time discounting by focusing on short 6-week treatment durations

The authors argue that the short time frame they present (6 weeks) means that discounting isn’t an issue. If individuals did not fully appreciate the timing was weeks–instead just considered generic time periods–then discounting could have played a role here. However, assuming that respondents did properly understand the nature of the question, discount rates would have a very small impact over 6 weeks and the findings can be attributable to non-linear utilities. This may be particularly relevant for treatments with fast-acting mechanisms of action. You can read the full paper here.