Rasch Measurement Theory's contribution to the psychometric properties of a co-created measure of health and wellness for Indigenous children and youth.

OBJECTIVES: To determine how Rasch Measurement Theory (RMT) methods can be used to assess the psychometric properties of the Aaniish Naa Gegii: the Children's Health and Wellbeing Measure (ACHWM) and Qanuippit. STUDY DESIGN AND SETTING: Indigenous children aged 8-18 years, from five communities, completed the 62-item ACHWM. We applied RMT methods to ACHWM data from 401 children (mean age 13.4 ± 3.4 years; 51% male) from across Ontario to examine how well the items captured the full range (±3 logit) of the concept of interest in each domain, targeted the needs of Indigenous children, and met the criteria for unidimensional and invariant measurement. RESULTS: RMT results indicated moderate-fit overall fit (raw χ2 = 809, P < 0.001). This model was further improved by aggregating the five response categories into three categories. All four domains showed excellent overall fit to the Rasch model (P > 0.05), with items covering between -4.51 and 6.02 logit, with no gaps along the theoretical continua. CONCLUSION: This study provides evidence that a set of conceptually derived items was able to produce a measure that fits the Rasch model. These results aid our understanding of wellness by establishing the clinical meaning of the scale scores.