Validation of the Digestive System Concept Scale for 7th‑Grade Students: Integrating Factor Analysis and Rasch Modeling

Abstract Understanding students' misconceptions in science requires instruments that are both pedagogically meaningful and psychometrically sound. This study presents a comprehensive validation of the 20‑item Digestive System Concept Scale (DSCS) administered to 7th‑grade students in Turkey. The scale was designed to identify persistent misconceptions about digestive processes, combining content validity from curriculum and expert review with two‑stage multiple‑choice items scored dichotomously. Data from 412 students were analyzed. Exploratory factor analysis (EFA) on tetrachoric correlations suggested one to two latent factors. Confirmatory factor analysis (CFA) using weighted least squares means and variance adjusted (WLSMV) estimation favored a two‑factor model (CFI = 0.997, TLI = 0.996, RMSEA = 0.009, SRMR = 0.070) over a one‑factor alternative (CFI = 0.978, TLI = 0.975, RMSEA = 0.024, SRMR = 0.076). Rasch modeling suggested unidimensionality (nonvital person left out reliabilities), and unidimension person reliabilities equals to 0. 706 while span for item difficulties within the range of -0.85 and 0.786 logits. The correlation between factors was high, suggesting that student responses are governed by a single underlying proficiency with two interpretable facets.. Six items exceeded standardized fit thresholds, but their mean‑square statistics remained acceptable; no pair of items showed residual correlations above 0.20. Together, the findings support reporting a single Rasch total score while retaining the two‑factor structure for interpretive purposes. We discuss implications for instrument design, instructional practice, and future research.