Development and quality assessment of the psychometric properties of the Self-Efficacy in Lifestyle Counselling scale (SELC 20+20) using Rasch analysis

Background: Globally as well as in Sweden, diseases that are caused by unhealthy lifestyle habits are the most common causes of death and disability. Despite guidelines that obligate all health care professionals to counsel patients about lifestyle, studies have shown that this is not prioritized within health care. One reason for this omission, among nurses, is a lack of confidence in knowledge and counselling skills. This study aimed to develop and provide a quality assessment of the psychometric properties of an instrument to measure self-efficacy in lifestyle counselling. Methods A measurement instrument, inspired by an existing American instrument following Bandura’s recommendations for the development of self-efficacy measures, was developed according to Swedish national guidelines for disease prevention. The instrument was revised after 18 kognitive interviews with nurses, student nurses and clinical experts and was administered to 310 nursing students at different education levels. The instrument was tested with Rasch model analysis with a focus on dimensionality, local dependency, targeting, reliability, response category functioning, Rasch model fit, and differential item functioning by age, gender, educational level and previous health care education. Results The development of the instrument resulted in 20 + 20 items, 20 about self-efficacy in knowledge and 20 about self-efficacy in the ability to counsel persons about their lifestyle. The analyses showed that knowledge and ability are two different, but related constructs and that ability is more demanding than knowledge. The findings indicate (considering dimensionality and local dependency) that all 20 items within the knowledge construct as well as the 20 items within the ability construct can be summed to obtain two separate but related total scores, where knowledge (reliability 0.91) is a prerequisite for ability (reliability 0.93). The items represented lower self-efficacy than reported by the respondents. The response categories functioned as expected, the Rasch model fit was acceptable, and there was no differential item functioning. Conclusions The SELC 20 + 20 was found to be easy to understand with an acceptable respondent burden, and the instrument showed good measurement properties. The instrument can be a useful tool in the professional education of health care personnel and clinically in health care.