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 stepw‐ise 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 exami‐ned 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.