Evaluation of the Structural Validity of the Work Instability Scale Using the Rasch Model

Area of Science:

• Occupational Health
• Psychometrics
• Rehabilitation Medicine

Background:

• The Work Instability Scale (WIS-23) is used to assess work-related upper extremity disorders.
• Evaluating the psychometric properties of the WIS-23 is crucial for accurate patient assessment.
• Rasch analysis provides a robust method for examining measurement properties of scales.

Purpose of the Study:

• To apply Rasch analysis to evaluate and refine the measurement properties of the 23-item Work Instability Scale (WIS-23).
• To develop an improved version of the WIS for use in worker compensation claimants with upper extremity disorders.

Main Methods:

• Secondary data analysis of a cross-sectional study involving 392 patients with upper limb injuries.
• Application of Rasch analysis to the WIS-23 data.
• Iterative item removal and splitting to achieve model fit.

Main Results:

• The initial WIS-23 showed significant misfit with the Rasch model.
• After refinement, a 20-item scale (WIS-20) met all Rasch model assumptions, including unidimensionality and local independence.
• The refined scale demonstrated absence of differential item functioning across key demographic and clinical factors.

Conclusions:

• Rasch analysis successfully refined the WIS-23 into a 20-item WIS (WIS-WREUD) with superior measurement properties.
• The 20-item WIS-WREUD exhibits excellent item and person fit, unidimensionality, and local independence.
• The WIS-20 offers potential for improved assessment of work-related upper extremity disorders, warranting further longitudinal validation.