INQ-15 cut-off scores for suicidal ideation screening of women with chronic, invisible illnesses.

In the interpersonal theory of suicide, perceived burdensomeness (PB) and thwarted belongingness (TB) are proximal triggers of suicidal ideation. Using the 15-item version of the Interpersonal Needs Questionnaire (INQ-15), suicidal ideation in psychiatric inpatients was predicted by the PB and TB scales, and cut-off scores were recommended. In this study, women (N = 942) who reported one or more chronic, invisible illnesses completed an online survey including the INQ-15 and the Suicide Behaviours Questionnaire-Revised (SBQ-R). PB and TB correlated significantly with SBQ-R total scores (r = 0.575 and 0.437, respectively; p < 0.01). In a Receiver Operating Characteristic analysis, scores of 17 for PB and 37 for TB maximized the correct classification of high-risk and low-risk participants, with slightly higher classification accuracy for PB than TB (AUCs = 0.781 and 0.701, respectively). These results support the INQ-15 scales in screening for suicidal ideation among chronically ill women.