Measuring What Matters: A Rasch-validated Instrument for Functional Sexual and Reproductive Health Literacy Among Ghanaian Adolescents

Background Functional sexual and reproductive health (SRH) literacy is fundamental to informed decision-making among adolescents. Yet existing measures hardly address the needs of low-literate populations in Sub-Saharan Africa. This study developed and validated a test of Functional Literacy in SRH (TOFL-SRH), a contextually grounded instrument designed to assess functional SRH literacy among Ghanaian adolescents with varying literacy levels. Methods A cross-sectional survey was conducted among 613 adolescents from public basic schools. The 37-item TOFL-SRH, scored dichotomously, was evaluated using the Rasch model. Analyses included item difficulty and person ability estimation, infit and outfit statistics, reliability and separation indices, and principal components analysis (PCA) of standardized residuals to assess unidimensionality. Local independence was evaluated using MADaQ3 and residual correlations. A Wright map was constructed to examine item, person targeting. Known-group validity was assessed using Welch’s t -test and effect sizes for grade level, gender, and age. Results The instrument demonstrated strong unidimensionality, with only the first contrast in the PCA exceeding an eigenvalue of 2.0. Local independence was supported by a low MADaQ3 value (0.054) and no item-pair residual correlations above 0.20. Item difficulty estimates ranged from − 1.74 to + 1.76 logits, emphasizing broad coverage of the latent trait. Fit statistics fell within acceptable thresholds, and item reliability (0.99) and person reliability (0.77) indicated stable measurement. The Wright map demonstrated good alignment between item difficulty and student ability levels. Known-group validity showed significant differences by grade level (p < 0.001) and age (p = 0.003). The non-significant difference by gender (p = 0.886), supports the instrument’s discriminative and unbiased functioning. Conclusion The TOFL-SRH is a psychometrically robust, culturally appropriate instrument for evaluating functional SRH literacy among low-literate adolescents. The strong measurement properties and practical relevance make it suitable for identifying literacy gaps, guiding SRH education, and evaluating interventions in resource-limited settings.