Protocol for the development of a transdiagnostic core outcome set for mental health disorders in adults: the Patient Important Outcomes in Psychiatry (PIO-Psych) Initiative

INTRODUCTION: Mental health problems are important causes of disability and economic costs worldwide. Randomised clinical trials examining the treatment of mental health disorders measure heterogeneous outcomes, causing difficulties in data synthesis, interpretation and translation into clinical practice. The aim of the Patient Important Outcomes in Psychiatry (PIO-Psych) Initiative is to develop an overarching, transdiagnostic research-based and consensus-based core outcome set for adult mental health disorders. METHODS AND ANALYSIS: The development of the PIO-Psych transdiagnostic core outcome set will include three phases: (1) a systematic scoping review of the literature to develop the initial list of outcomes for the Delphi study; (2) a Delphi study in three rounds including people with lived experience of mental health disorders and their relatives, clinicians, researchers and others (administrators, mental healthcare policymakers, philosophers); (3) a hybrid consensus meeting to agree on the final overarching, transdiagnostic core outcome set and corresponding time points of assessment of each outcome. ETHICS AND DISSEMINATION: Ethical approval is not applicable to this study according to the Research Ethics Committee of the Capital Region of Denmark, as it is not an interventional study. All data will be reported anonymously, and it will not be possible to identify study participants. Results will be disseminated via stakeholder and research networks and peer-reviewed publications. TRIAL REGISTRATION DETAILS: The PIO-Psych Initiative was pre-registered with COMET (Core Outcome Measures for Effectiveness Trials) on 17 May 2024 (https://www.comet-initiative.org/Studies/Details/3125).