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The corner answers in time trade-off, TTO, i.e. non-trading (NT) and assigning utility of -1 — all-intrading (AIT), occur frequently and impact the resulting models and value sets. Non-trading worsens the discriminatory power for mild health states. All-in-trading means the average utility estimates are biased upwards (models with censoring help but require parametric assumptions). We aim to test if modifying the TTO protocol lowers the frequency of NT/AIT.

We will use three arms in computer assisted face-to-face TTO data collection: a control arm (resembling cTTO) and two experimental arms (approx. 150 respondents each). We will test modifications: e.g., asking respondents if finer granularity would get them to trade; or improving the alternative with the diseased state (by adding some years in full health) instead of worsening the full health alternative; or use a diseased state in both compared profiles in the worse-than dead domain. We will compare the proportion of NT/AIT between the arms and see if modifications improve the association between state severity and utility in the worse-than-dead domain.