LAUSR

OBJECTIVE To investigate the targeting, scaling, and structural validity of the Work Limitation Questionnaire (WLQ) by Rasch analysis. DESIGN Secondary data analysis SETTING: Tertiary care hospital. PARTICIPANTS The data were sourced from an upper limb specialty clinic of injured workers by convenience sampling method and from a national randomized control trial (RCT) investigating two surgical options for rotator cuff repair by formal, randomized selection. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURE(S) Work Limitation Questionnaire 25-item version (WLQ-25). The WLQ contains 25 items measuring a client's ability to perform specific job demands on a 5-point ordinal response scale ranging from 0 as difficulty none of the time to 4 as difficulty all the time. The average of all 25 items is used as the total score, ranging from 0 to 4, where higher index scores indicate greater difficulty performing daily work. Subscales are used to assess Time Management (TM), the Physical Demands (PD), the Mental-Interpersonal Demands (MI), and the Output Demands (OD). RESULTS The Rasch analyses performed on the dataset included the test of fit of residuals, ordering of item thresholds, Person separation index, differential item functioning (DIF), dependency, and unidimensionality. The partial credit model was selected for the current Rasch analysis since the likelihood ratio test was significant at both the overall questionnaire and the subscale level (p<0.001). The WLQ-25 did not fit with the Rasch model (χ2 = 1715.58, df = 125, p < 0.001) and most of the thresholds were disordered. A series of steps were undertaken to improve the fit statistic including item reduction (6 items), and responses merging (9 items). DIF was absent in the revised scale based on sex, age, employment hour, and type of employment. Only 3 revised subscales Including Physical Demands, Mental Demands and Interpersonal Demands subscales show acceptable fit to the Rasch model. CONCLUSIONS The WLQ-25 demonstrated substantial misfit from the Rasch model which could not be fully mediated. The revised Physical Demands, Mental Demand sand Interpersonal Demands subscales could be used as to assess these constructs.