Internal consistency and construct validity of a questionnaire measuring representations related to work disability

Introduction
Health, illness and treatment representations have been described as key factors for return to work. An adaptation of the 9 dimensions of the Revised Illness Perception Questionnaire has been elaborated to better assess the representations of workers on sick leave due to musculoskeletal disorders (MSDs). Consequently, a validation study was needed to evaluate internal consistency and construct validity of the adapted questionnaire (IPQR-WD).

Methods
A cross-sectional study was conducted from December 2010 to June 2011 in Montreal region, Canada. Participants (n=41 males and females, French speaking) in the chronic pain phase (between 3 months and a year of absence from work due to MSDs) were recruited in work rehabilitation centers. The IPQR-WD and the following related measures for the construct validity were administered: Pain Catastrophizing Scale, Tampa Scale for Kinesiophobia, Pain Beliefs and Perceptions Inventory, Pain Disability Index, Psychiatric Symptoms Index, Self-Efficacy for Return to Work Scale, Implicit Models of Illness Questionnaire and a Visual Analog Scale for pain intensity.

Results
Calculations of Cronbach’s alphas revealed good to excellent internal consistency for each dimension (from 0.61 to 0.88), lowest score being associated to the Cyclical Timeline scale which contains only 4 items. Multiple regression analyses with each dimension of the IPQR-WD and variables found to be significantly associated in a preliminary correlation matrix explained a good proportion of the variance (r2 from 0.40 to 0.74) for each dimension, except for Cyclical timeline, which correlations became non significant after adjusting for gender, age and length of sick leave.

Discussion
Results support the internal consistency and construct validity of the IPQR-WD with an MSD population. Strong correlations were found with six related measures which support the unique contribution of the IPQR-WD as one simple questionnaire that can assess representations related to work disability and may facilitate their systematic evaluation in research and in clinic.