Construct validity of the Quebec Back Pain Disability Scale: a factor analytic and Rasch study

Area of Science:

• Psychometrics
• Health Outcomes Research
• Rehabilitation Science

Background:

• Previous studies indicated uncertain unidimensionality of the Quebec Back Pain Disability Scale (QBPDS).
• The QBPDS is widely used for assessing disability in patients with low back pain.

Purpose of the Study:

• To investigate the dimensionality and internal construct validity of the QBPDS.
• To apply advanced psychometric methods to evaluate the QBPDS structure.

Main Methods:

• Secondary analysis of cross-sectional data from 201 chronic low back pain patients.
• Utilized Confirmatory Factor Analysis (CFA), Exploratory Factor Analysis (EFA), and Rasch analysis.
• Examined single-factor and bi-factor solutions, followed by Rasch analysis on the QBPDS data.

Main Results:

• Confirmatory Factor Analysis (CFA) did not yield a satisfactory one-factor solution.
• A bi-factor solution showed good fit, and Rasch analysis indicated essential unidimensionality after removing four underfitting items.
• The 16-item scale demonstrated acceptable fit to the Rasch model.

Conclusions:

• The Quebec Back Pain Disability Scale (QBPDS) demonstrates essential unidimensionality.
• Provisional use of the full QBPDS and its global score is suggested, pending further validation.
• Removing specific items may enhance the scale's metric quality for chronic low back pain assessment.