Exploring the involvement of people with lived experience of mental disorders in co-developing outcome measures: a systematic review.

People with lived experience of mental health difficulties have highlighted that research outcomes do not capture issues they feel are important. This mismatch might affect the validity of trials, such that beneficial effects could be missed or results could be counted as a benefit when they are not. Co-development of patient-reported outcome measures ensures patient perspectives are captured adequately. To identify mental health outcome measures that meet a strict definition of being co-developed and to describe the methods and quantity of involvement at each pre-defined stage of measure co-development, we searched five electronic databases (MEDLINE, Web of Science, Scopus, PsycINFO, and Embase) for relevant papers, alongside a search of the non-peer reviewed literature and handsearching. The study was registered on PROSPERO (CRD42024520941). Retrieved papers were independently screened and quality was assessed following PRISMA guidelines. Extracted data were synthesised narratively. The search identified 23 mental health outcome measures from 34 papers. The most frequent types of involvement to co-develop outcomes were service-user researchers and lived experience groups as advisors undertaking activities such as leading qualitative exercises, but there were gaps. Many benefits were reported such as increased relevancy and acceptability of the measures. Based on these findings, recommendations for methods and a novel scale for judging quantity of involvement for co-development were identified, but challenges for co-development remain. The reviewed papers show that co-development is possible and could provide more relevant and meaningful outcomes for clinical practice and research.