Measuring Productivity Costs in Patients With Musculoskeletal Disorders: Measurement Properties of the Institute for Medical Technology Assessment Productivity Cost Questionnaire

Abstract

Background: The Institute for Medical Technology Assessment Productivity Cost Questionnaire (iPCQ) was recently developed to cover all domains of productivity costs; absenteeism, presenteeism and productivity costs related to unpaid work. The original iPCQ has not been tested with respect to neither content or construct validity, nor reliability, and there is no Norwegian version of the questionnaire.

Objectives: To translate and cross-culturally adapt the iPCQ into Norwegian and to test its measurement properties among patients with musculoskeletal disorders.

Methods: Translation and cross-cultural adaptation was conducted according to guidelines, and measurement properties were investigated using a cross-sectional design including a test-retest assessment. Patients with musculoskeletal disorders were recruited from secondary care. Data quality, content validity (10 patients evaluated comprehensibility, 2 researchers and 1 clinician evaluated relevance and comprehensiveness), construct validity (factor analysis, internal consistency, divergent hypothesis testing), and test-retest reliability (intraclass correlation coefficient two-way random average agreement, Cohen's unweighted kappa) were assessed.

Results: In total, 115 patients with a mean age (SD) of 46 (9) years were included, and 62 responded to the retest. The questionnaire was feasible, with little missing data and no floor or ceiling effects. Content validity displayed good comprehensibility and relevance and sufficient comprehensiveness. Factor analysis revealed a 3-component solution accounting for 82% of the total variance; items loaded as expected and supported the original structure of the iPCQ. Internal consistency was acceptable for the 3 components of productivity cost, with an inter-item correlation ranging from 0.42 to 0.62. Further, a total of 91% of our hypotheses were verified. The intraclass correlation coefficient values ranged from 0.88 to 0.99 for all items except one; kappa ranged from 0.61 to 0.92, indicating overall good reliability of the questionnaire.

Conclusions: The Norwegian iPCQ showed good measurement properties among patients with musculoskeletal disorders from secondary care in Norway. We therefore recommend the iPCQ as a useful tool for measuring productivity costs in patients with musculoskeletal disorders.

Keywords: measurement properties; musculoskeletal disorders; productivity costs.