Abstract
BACKGROUND: Middle and late adolescence is the period in a person's life that is most vulnerable to mental health problems. To enable an evidence base that can support policies to prevent such problems, it is crucial to have good quality, reliable, and accurate measurement tools for mental well-being. One of them is the Short Warwick-Edinburgh Mental Well-Being Scale (SWEMWBS). This study aimed to test the psychometric properties of the SWEMWBS on a large sample of adolescents aged 16 to 19 from the United Kingdom (UK) (N = 8,090). Data were from four waves of the longitudinal panel study Understanding Society. METHODS: The analysis was conducted using Item Response Theory (IRT), which is the most appropriate method for testing psychometric properties. The Graded Response Model (GRM) was applied to the data. The reliability and criterion validity of the SWEMWBS were also examined. RESULTS: The presented results confirm the very good psychometric properties of the SWEMWBS amongst adolescents aged 16 to 19 years. The assumptions for the use (unidimensionality, local non-independence, monotonicity) of IRT were met. The results of GRM showed very high discriminant power for all items. The five-category response scale performed optimally; however, differences were found between points on the response scale both between and within items. In general, the scale as a whole showed very good functioning, but particularly in the negative values of mental well-being. CONCLUSIONS: The SWEMWBS was confirmed as a concise, reliable, and valid instrument for measuring mental well-being among older UK adolescents.