Development of the coreHEM mental health patient‐reported outcome measure – A novel mental health outlook measure for people with haemophilia

INTRODUCTION: Currently, no quality-of-life instrument exists that captures the full experience of the mental health outlook (MHO), a coreHEM core outcome, in people with haemophilia, including the potential transformational experience of receiving gene therapy. AIM: To describe the methods used to develop a content validated patient-reported outcome measure (PROM) that measures MHO for people with haemophilia.