Psychometric Evaluation of Sinhala and Tamil Measures of Suicidal Behavior and Interpersonal Suicide Risk Constructs in Sri Lanka

Background: Valid and culturally appropriate instruments are essential for suicide research and risk screening. This study evaluated the psychometric properties of the Sinhala and Tamil versions of the Suicide Behaviors Questionnaire-Revised (SBQ-R), Interpersonal Needs Questionnaire-10 (INQ-10), and Acquired Capability for Suicide Scale-Fearlessness About Death (ACSS-FAD), which assess constructs of the Interpersonal Theory of Suicide (IPTS). Methods: In this cross-sectional study, 551 university students (409 Sinhala-speaking, 142 Tamil-speaking) and 98 patients presenting with self-harm completed the measures. Structural validity, reliability, convergent validity, known-group validity, measurement invariance, and receiver operating characteristic analyses were performed. Results: The SBQ-R demonstrated a unidimensional structure, good internal consistency (ordinal α = 0.86–0.92), language and gender invariance, and satisfactory convergent and known-group validity. The original seven-item ACSS-FAD performed poorly, whereas a four-item version demonstrated satisfactory psychometric properties. INQ-10 did not support the hypothesized two-factor structure, with relatively better support for a bifactor model. The SBQ-R discriminated between students and patients presenting with self-harm (AUC = 0.716, 95% CI = 0.656–0.777), with improved discrimination among patients reporting suicidal intent (AUC = 0.876, 95% CI = 0.820–0.931). The established cut-off of ≥7 was supported. Conclusions: The Sinhala and Tamil SBQ-R demonstrated good psychometric properties and are suitable for suicide research and risk screening in Sri Lanka. The four-item ACSS-FAD appears preferable to the original version, whereas INQ-10 subscale scores should be interpreted cautiously. These findings support further research on suicidal behavior and evaluation of IPTS-based hypotheses in clinical and community populations in Sri Lanka.