Evaluation of the Structural Validity of the Work Instability Scale Using the Rasch Model.
Ze Lu, Joshua I Vincent, Joy C MacDermid
PMID 33778476WHAT IT FOUND
The 23-item Work Instability Scale fits poorly for upper-limb injury workers.
Removing three items creates a 20-item version that measures work instability accurately and allows valid statistical comparison of scores.
Key findings
01The original 23-item scale showed poor fit to the statistical model, with three items identified as problematic and removed.
02The revised 20-item scale demonstrated acceptable fit, unidimensionality, and local independence in the study sample.
03The study provides a conversion table to transform raw scores into interval-level scores, enabling valid statistical analysis of change.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTs
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What it does not show
The study only included workers with upper limb injuries, so the results may not apply to other conditions or body regions. Rasch analysis identifies which items do not fit but does not explain why; the removed items might still capture relevant clinical experiences. The study did not assess the responsiveness of the new 20-item scale to change over time.
Declared interests
None reported.
The easy way to misread this
Do not assume the removed items (1, 19, and 23) are clinically irrelevant. They were excluded because they did not fit the statistical model, not because they fail to capture important patient experiences.