Scale development and validation followed all relevant consensus-based standards for the selection of health measurement instruments (also known as COSMIN guidelines).39 We developed a 7-item scale by extracting core diagnostic items from 6 lifetime DSM5-compatible diagnoses: social phobia, panic disorder, agoraphobia, obsessive compulsive disorder, post-traumatic stress disorder, major depressive episode, and symptoms of suicidality from the SSAGA. Suicidality was added because it can reflect depression and anxiety not captured by other items. Because suicide attempts can also contain impulsive, externalizing elements, we only included attempts that: a) took place in the context of depression; b) did not take place in the context of alcohol or drug use, psychosis, or mania; and c) were preceded by at least 7 days of premeditation. Only symptoms and diagnoses occurring free of the influence of alcohol, drugs, changes in medication, co-occurring illnesses, or post-partum conditions contributed to the Internalizing Scale total score. Higher scores indicated more internalizing problematic characteristics.
