The development and psychometric validation of the self-efficacy and performance in self-management support (SEPSS) Instrument

__Aim:__ To develop and psychometrically test the self-efficacy and performance in self-management support (SEPSS) instrument. __Background:__ Facilitating persons with a chronic condition to take an active role in the management of their condition, implicates that nurses acquire new competencies. An instrument that can validly and reliably measure nurses' performance and their perceived capacity to perform self-management support is needed to evaluate current practice and training in self-management support. __Design:__ Instrument development and psychometric testing of the content and construct validity, factor structure and reliability. __Methods:__ A literature review and expert consultation (N = 17) identified the content. The items were structured according to the Five-A's model and an overarching category of 'overall' competencies. The initial instrument was tested in a sample of 472 nurses and 51 nursing students from Belgium and the Netherlands, between June 2014-January 2015. __Results:__ Confirmatory factor analyses revealed satisfactory fit indices for the six-factor structure. Discriminating power was demonstrated for subgroups. The overall internal consistency (Cronbach's alpha) was high both for the self-efficacy and the performance items. The test-retest intra-class correlation coefficients were good. __Conclusion:__ The SEPSS instrument is a 36-item, Likert-scaled self-reporting instrument with good content and construct validity, and good internal consistency reliability and good test-retest reliability. Therefore, it is a promising instrument to measure self-efficacy and performance with regard to self-management support.