Background Adherence to exercise interventions is often suboptimal, despite numerous studies documenting barriers and facilitators. Usability may be a critical yet underexplored determinant of adherence. This study aimed to develop and assess the psychometric properties of the Intervention Usability Scale for Exercise (IUSE). Methods Item generation and content validation involved cognitive interviews and feedback from eight exercise intervention stakeholders and ten target users from the general public. Subsequently, 526 target users from University, Qualtrics and Prolific participant panels assessed exercise programs through an online survey. Dimensionality was assessed using PCA, EFA, and bifactor models. Item reduction was conducted through Item Response Theory (IRT) graded response models, assessing discriminability, item information levels/patterns and differential item functioning. Test-retest reliability was assessed using Pearson’s r . Subsequently, short vs. original scale versions were compared. Finally, evidence of criterion, convergent, and discriminant validity was assessed. Results Thirty-six items were initially included, with 16 removed due to low test-retest reliability and factor loadings (r < 0.50). A 3-factor structure emerged from EFA, PCA, and bifactor models: Value, Ease, and Social. Iterative IRT evaluation led to 12 item removals, resulting in 8 final items across three subscales. Validity analyses indicated good convergent (e.g., r = 0.79 with Intervention Appropriateness Measure, r = 0.65 with Intervention Usability Scale), criterion (e.g., r = 0.71 with Net Promoter Score and 0.75 with intention measures), and discriminant validity ( r = 0.42 with External Motivation), along with satisfactory internal consistency (Cronbach's alpha: 0.79-0.84). Conclusions The IUSE scale demonstrated promising psychometric properties. Application of the scale with collection of actual uptake/adherence data is needed to assess predictive validity.
Mørtvedt et al. (Mon,) studied this question.