Psychometric evaluation of the MEDication Literacy Assessment in Geriatric Patients and Informal Caregivers (MED-fLAG) instrument using Rasch analyses in a sample of hospitalised older adults.

Background: Medication literacy is critical for older adults managing complex medication regimens, yet few measures have been developed specifically for this population. The MEDication Literacy Assessment of Geriatric patients and informal caregivers (MED-fLAG) was developed as a multidimensional self-reported measure for older adults and informal caregivers. The instrument uniquely captures skills related to both prescribed and non-prescribed medications, including herbal and nutritional supplements. Although the MED-fLAG previously demonstrated satisfactory content validity, further evaluation of its psychometric properties was warranted. Objectives: To evaluate the psychometric properties of the MED-fLAG using Rasch analyses. Methods: A cross-sectional study was conducted among French- and Dutch-speaking hospitalized older adults in Switzerland, Belgium, and the Netherlands. Hospitalized participants aged ≥ 65 years who had managed their medications for at least three months were included. Rasch modelling using the Partial Credit Model was applied to assess unidimensionality, item fit (goodness-of-fit), item hierarchy (item difficulty calibration), person separation reliability, and differential item functioning across language groups. Results: Among the 582 respondents, the mean age was 73.9 years, with a standard deviation of 11.4 years. Analyses were conducted on 563 responses, including 356 from the Dutch-speaking sample and 207 from the French-speaking sample. Rasch analyses supported the measurement properties of the Functional subscale (with 19 items) and Interactive subscale (with 13 items), including satisfactory unidimensionality, item fit, and reliability. However, the Critical subscale (with 21 items) displayed signs of multidimensionality and substantial differential item functioning across languages. Person separation indices fell below the recommended threshold, indicating moderate discrimination, and Wright maps highlighted the need for more challenging Interactive items and easier Critical items. Conclusions: These findings support the MED-fLAG as a promising instrument while underscoring the need for further refinement, particularly within the Critical medication literacy subscale. In the future, this standardized measure may support the formal assessment of medication literacy among older adults and informal caregivers to ensure that medication regimens align with patients' abilities. In the context of early hospital discharge, the MED-fLAG may provide valuable information to guide individualized care planning and help prevent medication-related problems. Future research should also explore the development of an optimized and potentially shorter version of the MED-fLAG to enhance feasibility in routine clinical practice. Further psychometric evaluation of a revised version of the MED-fLAG is needed before the instrument can be confidently recommended for research and clinical use.