Psychometric properties of the Warwick-Edinburgh Mental Wellbeing Scale-Intellectual Disability version (WEMWBS-ID)

Mental wellbeing, encompassing dimensions of hedonia (feeling good) and eudaimonia (functioning well), is considered a valuable resource for individuals and communities. The Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS; Tennant et al., 2007), a 14-item positively worded measure of mental wellbeing, has been extensively psychometrically validated within the UK and cross-culturally. However, it is yet to be validated for use with individuals with intellectual disabilities, a priority given the paucity of measures of mental wellbeing for this population. The aim of this study was to assess the psychometric properties of a newly adapted version of the WEMWBS and the Short 7-item WEMWBS (SWEMWBS) for individuals with mild to moderate intellectual disabilities (WEMWBS-ID/SWEMWBS-ID).The WEMWBS item wordings and response options were revised by clinicians and researchers expert in the field of intellectual disability, and a visual aid was added to the scale. The adapted version was reviewed by 10 individuals with intellectual disabilities. Individuals aged 16+ with mild to moderate intellectual disabilities were recruited using volunteer sampling. Data from three studies conducted in the UK were collated to evaluate the psychometric properties of the WEMWBS-ID (n=96) and additional data from a study conducted in Canada (n=27) was used in addition to the UK data to evaluate the SWEMWBS-ID (n=123). The WEMWBS-ID was administered by researchers via an online meeting using the screenshare function. A subsample (n=22) completed the scale twice for test-retest reliability. Furthermore, as a relationship between wellbeing and self-esteem has been demonstrated in previous research, 95 of the UK participants also completed an adapted 6-item version of the adapted Rosenberg Self-Esteem Scale (RSES) to assess convergent validity.The WEMWBS-ID demonstrated good internal consistency (α=0.86), excellent test-retest reliability (ICC=0.88) and good convergent validity (r=0.68) with the RSES. Confirmatory factor analysis supported the hypothesised one-factor structure and the measure demonstrated an adequate model fit. The SWEMWBS-ID showed poorer internal consistency (α=0.67), good test-retest reliability (ICC=0.67) and good convergent validity (r=0.61). The results from the confirmatory factor analysis indicated a good model fit.The results from this initial evaluation of the WEMWBS-ID and SWEMWBS-ID suggest that the scales have promising psychometric properties, when administered by a researcher to individuals with mild to moderate intellectual disabilities. The generalisability of the findings is limited by the sample size and sampling strategy and a further exploration of the scales with larger samples is warranted. Suggestions for future research are discussed.