A multimethod validation of the frequency of suicidal ideation inventory for adolescents in Peru

Background: Suicidal ideation assessment requires psychometrically robust measures, particularly in adolescent populations in which risk factors may differ from those of adults. This study examined the psychometric properties of the Frequency of Suicidal Ideation Inventory (FSII) in Peruvian adolescents. Methods: A cross-sectional study was conducted among 1211 adolescents (50.3% female; M = 14 years, SD = 1.53) from grades 1 to 5 in public schools in Lima (55.3%, surveys administered in Spanish) and Cusco (44.7%, surveys administered in Quechua). Data were collected using self-administered paper-based questionnaires, which included the Frequency of Suicidal Ideation Inventory (FSII), the Generalized Anxiety Disorder Scale (GAD-7), and the Patient Health Questionnaire (PHQ-9). Results: Confirmatory factor analysis (CFA) supported the unidimensionality of the scale with excellent fit indices [Comparative Fit Index (CFI) = 0.99, Tucker–Lewis Index = 0.99, Root Mean Square Error of Approximation = 0.017, Standardized Root Mean Square residual (SRMR) = 0.005] and high factor loadings (0.82–0.91). Complementing the CFA, Item Response Theory analyses further confirmed the structural robustness of the scale, with excellent model fit (97.6% of response patterns fit the graded response model), strong item discrimination parameters (α > 2.7), and well-targeted difficulty levels across the trait continuum. Measurement invariance testing demonstrated equivalent functioning across gender (girls vs. boys) and ethnolinguistic groups (Spanish-speaking vs. Quechua-speaking) (ΔCFI < 0.010, ΔSRMR < 0.030 at all levels). Moreover, the FSII showed strong convergent validity, with significant correlations with depressive symptoms (r = 0.68) and generalized anxiety (r = 0.65). Reliability was consistently high (ω = 0.90, H = 0.94, rxx = 0.82) and provided precise measurement at moderate-to-high levels of suicidal ideation. Conclusions: These results support the FSII as a psychometrically sound measure for assessing suicidal ideation among adolescents in Peru, with potential utility for identifying individuals at risk.