Background: If disability is the gap between what an individual can do and what that individual would like to be able to do, then measures that assess only current ability fall short of describing the impact of disability on the individual.
Objective: The aim of this study was to examine a potential measure of disability, the gap between current movement ability and preferred movement ability, as recorded with the Movement Ability Measure (MAM). This investigation was performed by establishing the relationship between self-perceived current ability and other measures and examining the evidence of convergence or divergence between the gap and other measures.
Design: This investigation was a descriptive study.
Methods: Thirty people who had multiple sclerosis and were ambulatory completed the MAM and 18 other measures of bodily function, activity, and participation. Item response theory methods were used to generate logit estimates of average current movement ability and separate abilities in the 6 dimensions of movement on the MAM. Pearson correlations were calculated between estimated abilities from the MAM and scores from measures expected to be associated with these estimated abilities, as well as between the MAM and additional measures in exploratory analyses of relationships.
Results: The average current ability and the separate dimensions correlated moderately to strongly (.5-.8) with many of the measures expected to be related and showed additional moderately strong correlations in exploratory analyses. The average gap between current ability and preferred ability correlated moderately with pain (-.56) and a scale of current ability (.46) but diverged from many of the measures.
Limitations: The limitations of this study included the lack of an intervention to assess the response of the gap to therapy and the use of multiple statistical tests with a small sample.
Conclusions: The evidence supports the convergent validity for current ability on the MAM but mostly the divergence of the gap. Additional research should compare the gap specifically with measures that assess patients' preferences when determining disability.