Finding functionality: Rasch analysis of the Functionality Appreciation Scale in community-dwelling adults in the US

Area of Science:

• Psychometrics
• Rehabilitation Medicine
• Disability Studies

Background:

• The Functionality Appreciation Scale (FAS) assesses appreciation for bodily functions, irrespective of physical limitations.
• Previous research established the FAS's reliability and convergent validity, but its structural validity via Rasch analysis was unexplored.

Purpose of the Study:

• To evaluate the structural validity of the Functionality Appreciation Scale (FAS) using Rasch Measurement Theory.
• To assess the psychometric properties of the FAS, including item and person fit, targeting, unidimensionality, and reliability.

Main Methods:

• Recruited 567 community-dwelling adults, including 14 with spinal cord injury (SCI).
• Administered the FAS and analyzed data using Rasch Measurement Theory, examining item/person fit, unidimensionality, PSR, LID, PCAR, and DIF.
• Modified the FAS by rescoring 3 items and deleting 1 item based on initial analysis.

Main Results:

• The 6-item FAS demonstrated good person and item fit (except item 4) and confirmed unidimensionality.
• Person Separation Reliability (PSR) was 0.75, indicating moderate ability to differentiate individuals.
• A significant ceiling effect (28.04%) and mean person location indicated the FAS is too easy for the studied population.

Conclusions:

• The Rasch-based 6-item FAS exhibits good structural validity, unidimensionality, and fit.
• The scale requires more difficult items to enhance targeting and improve reliability for broader application.
• Further development is recommended to optimize the FAS for accurately measuring functionality appreciation across diverse populations.