Objectives Standard economic evaluation methods assume that quality-adjusted life years (QALYs) have equal social value, regardless of recipient. However, evidence suggests that people place greater social value on health gains for children. This study examines the factors driving age-related preferences for health gains. Methods Think-aloud, semi-structured interviews were conducted with Australian adolescents (n=7), non-parents (n=11), parents with healthy children (n=8) and parents of children with health conditions (n=15). Participants completed Person Trade-Off (PTO) and attitudinal questions about resource allocation for improvements in life extension, mental health, mobility, and pain/discomfort choosing between interventions for adults (ages 40 or 55) and younger people (ages one month to 24). Results Eleven themes emerged, illustrating participants’ complex reasoning. They considered differences in the impact of health loss at various ages, with difficulty envisaging mental health impacts for very young children. Emotional responses were strongest around children in pain. Adolescents tended to prioritize younger people, while parents often emphasized adults’ caregiving role. Most participants prioritized based on age in PTO questions, though some adults objected to prioritizing healthcare based on age. Conclusion Choices were shaped by perceptions of the impact of the health states. These findings provide insight into interpreting quantitative results from PTO tasks.

I have read the journal's policy and the authors of this manuscript have the following competing interests: [ ND, RN, TPA and TPE are all members of the EuroQol group. This does not alter our adherence to PLOS one policies on sharing data and materials]

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0302886

Yes ND, TPE, CB, RN - Medical Research Future Fund (MRFF) Grant number APP1200816 https://www.health.gov.au/our-work/medical-research-future-fund AD- EuroQol Research Foundation grant number 348-PHD https://euroqol.org/ The funders did not and will not have a role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

University of Melbourne human ethics committee [Reference number: 2023-24869- 47516-7]. Informed consent was obtained via a self-complete online questionnaire.

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The data in this study consists of quotes extracted from participant transcripts. These quotes are included within the manuscript and the Supporting Information (S2 Table). Consent from participants was obtained specifically for the use of these quotes in the study. However, full transcripts are not made publicly available as participant consent was not obtained to share the complete transcripts with the public.