Co-calibration of deliberate self harm (DSH) behaviours: towards a common measurement metric.

The purpose of this study was to co-calibrate items from different deliberate self-harm (DSH) behavioural scales on the same measurement metric and compare cut points and item hierarchy across those scales. Participants included 568 young Australians aged 18-30 years (62% university students, 21% mental health patients, and 17% community volunteers). Six DSH scales (containing 82 items) were administered, namely, Self-Injury Questionnaire Treatment Related (SIQTR), Self-Injurious Thoughts and Behaviours Interview (SITBI), Deliberate Self-Harm Inventory (DSHI), Inventory of Statements About Self-Injury (ISAS), Self-Harm Information Form (SHIF) and Self-Harm Inventory (SHI). Data were co-calibrated onto an underlying metric using the Rasch measurement model. The resulting calibration shows that the different scales occupy different ranges on the hierarchy of DSH methods with prevalence estimates ranging from 47.7 to 77.1%. A raw score conversion table is provided to adjust prevalence rates and to equate cut points on the six scales. A Rasch-validated hierarchy of DSH behaviours is also provided to inform the development of DSH nomenclatures and assist clinical practice.