Using Classical Test Theory to Determine the Psychometric Properties of the Italian Version of the Feeding/Swallowing Impact Survey

Background/Objectives: The Italian version of the Feeding/Swallowing Impact Survey (FS-IS-IT) is an 18-item caregiver self-report questionnaire assessing the impact of paediatric feeding disorders (PFDs) on health-related quality of life (HR-QoL). The present study sought to evaluate its psychometric properties using Classical Test Theory (CTT), following COSMIN (COnsensus-based Standards for the selection of health Measurement INstruments) guidelines and criteria. Methods: A total of 145 caregivers of children with PFD of various etiologies were recruited (median age: 60.0 months; IQR: 35.8–108.0), of whom 134 provided sufficiently complete data for psychometric analysis. Structural validity was determined using exploratory factor analysis. Internal consistency was assessed using Cronbach’s alpha coefficient, McDonald’s ω, and inter-item correlations. Hypothesis testing was conducted using Mann–Whitney U-tests and correlation analysis, while interpretability was examined by assessing floor and ceiling effects. Results: Factor analysis indicated that the FS-IS-IT is a unidimensional measure, with an adequate total variance explained of 60.1%. The FS-IS-IT has moderate structural validity, good internal consistency with some evidence of item redundancy, strong construct validity as supported by hypothesis testing, and no floor and ceiling effects. Conclusions: These findings suggest that the FS-IS-IT is a promising caregiver self-report measure for evaluating HR-QoL in PFD. Further validation is recommended to assess potential item redundancy and to examine the dimensionality of the FS-IS-IT using item response theory. Conversely, although the Italian version of the FS-IS demonstrated encouraging psychometric properties, it could be further strengthened in future studies by revising ambiguous items, refining response formats, and removing misfitting items.