The adaptation of a Danish version of the Pain Self-Efficacy Questionnaire: reliability and construct validity in a population of patients with fibromyalgia in Denmark.

The aim of this study was to translate, culturally adapt and evaluate the psychometric properties of the Pain Self-Efficacy Questionnaire (PSEQ) in a population of patients with fibromyalgia in Denmark. The study sample included 102 patients diagnosed with fibromyalgia referred to a specialist clinic. The PSEQ was translated and adapted to a Danish setting using a standard stepwise forward-backward translation procedure, followed by initial testing and focus group interview. Reliability was examined by analysing internal consistency and test-retest agreement. Construct validity was examined by investigating dimensionality, targeting, local independence, category functioning and differential item functioning (DIF). Reliability was high: Cronbach's alpha 0.88, test-retest correlation 0.93, intraclass correlation coefficient (ICC) 0.89 and item-total correlations 0.44-0.70. Factor analyses and item response (IRT) models indicated unidimensionality, and the PSEQ-DK was well targeted to the sample. High interitem correlation was observed between two items, indicating local dependence, and item misfit and DIF were observed for a few items. However, the overall fit of the scale to a single-factor model and IRT models supported acceptable construct validity. The PSEQ-DK showed acceptable psychometric properties and can therefore represent a reliable and valid measure for evaluating self-efficacy in patients with fibromyalgia in Denmark.