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

Introduction: The Functionality Appreciation Scale (FAS) measures an
individual's appreciation for the functions their body can perform,
regardless of the individual's physical limitations. Prior studies
reported on internal consistency, test-retest reliability, convergent
validity, and exploratory or confirmatory factor analyses, but Rasch
analysis has not yet been performed to evaluate the structural validity of
the FAS. Methods: We recruited community-dwelling adults at the
Minnesota State Fair and through contact lists of participants identifying
interest in research done in the Brain Body Mind Lab (University of
Minnesota). Community-dwelling adults with spinal cord injury (SCI)
completed the FAS over Zoom. We analyzed the FAS using Rasch Measurement
Theory, which produced the following outputs: item, and person fit,
targeting, unidimensionality, person separation reliability (PSR), local
item dependence (LID), principal component analysis of residuals (PCAR),
and differential item functioning (DIF). Results: We recruited
567 participants (average age 52.15 ± 17.5 years, 63.84% women), among
which 14 adults with SCI. After rescoring 3 items and deleting 1 item, the
FAS had good person and item fit (except item 4). The PCAR and subsequent
paired t-tests (3.53%) confirmed the unidimensionality of the
scale. There was no DIF and only one item pair had LID (item 5-6). PSR was
0.75, reflecting a capacity to differentiate groups of people with high or
low functionality appreciation levels. However, there was a significant
ceiling effect (28.04%) and the person mean location was 3.06 ± 2.07
logits, indicating the FAS is too easy for community-dwelling adults in
the US. Discussion: The 6-item Rasch-based FAS demonstrated
unidimensionality, good item fit (except item 4) and person fit, but the
FAS will require more difficult items to be added to improve the targeting
of the scale, and better reliability.