Rasch validation of a new scale to measure dependency in arm use in daily life: the Upper Limb Lucerne ICF-based Multidisciplinary Observation Scale (UL-LIMOS)
Authors: Van de Winckel Ann , Ottiger Beatrice , Veerbeek Janne Marieke , Nyffeler Thomas , Vanbellingen Tim 
Published: January 2023

AbstractIntroductionAbout 77% of adults with stroke have upper limb impairments. Many upper limb measures are available for adults with stroke to measure the impairment and activity level of the affected limb. However, an observational scale focused on assessing dependency in upper limb use during daily life activities (as opposed to testing in laboratory settings) is lacking. To bridge this gap, we have developed a new 5-item “Upper Limb Lucerne ICF-based Multidisciplinary Observation Scale (UL-LIMOS)”, which assesses dependency on others during affected arm use in daily life in adults with stroke. As a next step in the psychometric analysis, we evaluated the unidimensionality and structural validity of the UL-LIMOS with Rasch Measurement Theory.MethodsThis is a single-center cross-sectional study in adults with (sub)acute stroke. We applied Rasch Measurement Theory (RMT) to analyze the structural validation and unidimensionality of the new UL-LIMOS. We chose a polytomous partial credit model using the Rasch Unidimensional Measurement Model (RUMM) 2030 software. The outputs provide evidence of unidimensionality, item and person fit, overall fit, principal component analysis of residuals (PCAR), person separation reliability (PSR), as well as residual item correlations to identify local item dependence. Person mean location, floor and ceiling effects identify proper targeting.ResultsWe recruited 407 adults with (sub)acute stroke (median age 63 years, 157 women). All items and persons fit the Rasch model, and the PSR of 0.90 indicates that clinicians and researchers can reliably use the scale for individual decision-making. There were small floor (2.70%) and ceiling (13.00%) effects. The average person mean location was 1.32 ± 2.99 logits, indicating that the items were too easy for this group of adults with (sub)acute stroke. The PCAR’s eigenvalue was 2.46 with 49.23% explained variance. Further analysis of pairedt-tests revealed that 0.89% of person locations were significantly different when comparing the two subtests formed based on positive and negative loadings on the first principal component, thereby confirming the unidimensionality of the scale. One pair of items related to “arm and hand use” and “fine hand use” showed residual item correlations.DiscussionThe new Rasch-based UL-LIMOS is a valid ICF-based observation scale at the ICF-participation level, to evaluate dependency during upper limb use in daily life in adults with stroke. The UL-LIMOS would be a valuable addition to the core assessments of adults with (sub)acute stroke in hospitals and rehabilitation centers. Further analysis is needed to generalize our findings to adults with chronic stroke who have returned to their home setting, and in other countries to account for cultural differences. Targeting could be improved in the future. Additional psychometric analyses, such as sensitivity to change, are warranted. A comparison of the UL-LIMOS data with self-reported measurements or accelerometers could potentially lead to changes to the core datasets recommended for the evaluation of adults with stroke.