RESUMEN
This research aims to create and evaluate an assessment tool termed Older Adults' First Aid Knowledge Scale, which measures the knowledge and attitude of Iranian grandparents about first aid. In accordance with COSIM guidelines, 485 individuals in southern Iran completed the instrument as part of a psychometric investigation. Rasch partial credit model (PCM), exploratory factor analysis (EFA), confirmatory factor analysis (CFA), and receiver operating characteristic (ROC) analysis were used to analyze the results. The final version of OFAKS consisted of 18 items that were validated through EFA, CFA, and item response theory (IRT) analysis. All items showed measurement invariance and consecutive response groupings in the predictable order, and the instrument had strong internal consistency. Although Rasch's analysis demonstrated the significance of OFAKS, further investigations and testing in different settings are required to confirm the validity of the tool.