Article

PURPOSE: To evaluate the conformity of the Arm Activity measure (ArmA) passive
function sub-scale to the Rasch model. METHODS:
A consecutive cohort of patients
(n = 92) undergoing rehabilitation, including upper limb rehabilitation and
spasticity management, at two specialist rehabilitation units were included.
Rasch analysis was used to examine scaling and conformity to the model. Responses
were analysed using Rasch unidimensional measurement models (RUMM 2030). The
following aspects were considered: overall model and individual item fit
statistics and fit residuals, internal reliability, item response threshold
ordering, item bias, local dependency and unidimensionality. RESULTS: ArmA
contains both active and passive function sub-scales, but in this analysis only
the passive function sub-scale was considered. Four of the seven items in the
ArmA passive function sub-scale initially had disordered thresholds. These items
were rescored to four response options, which resulted in ordered thresholds for
all items. Once the items with disordered thresholds had been rescored, item bias
was not identified for age, global disability level or diagnosis, but with a
small difference in difficulty between males and females for one item of the
scale. Local dependency was not observed and the unidimensionality of the
sub-scale was supported and good fit to the Rasch model was identified. The
person separation index (PSI) was 0.95 indicating that the scale is able to
reliably differentiate at least two groups of patients. CONCLUSIONS: The ArmA
passive function sub-scale was shown in this evaluation to conform to the Rasch
model once disordered thresholds had been addressed. Using the logit scores
produced by the Rasch model it was possible to convert this back to the original
scale range. Implications for Rehabilitation The ArmA passive function sub-scale
was shown, in this evaluation, to conform to the Rasch model once disordered
thresholds had been addressed and therefore to be a clinically applicable and
potentially useful hierarchical measure. Using Rasch logit scores it has be
possible to convert back to the original ordinal scale range and provide an
indication of real change to enable evaluation of clinical outcome of importance
to patients and clinicians.

Langue : ANGLAIS