A Rasch Analysis of the Personal Well-Being Index in School Children Adrian J. Tomyn 1 , Mark A. Stokes 1 , Robert A. Cummins 1 and Paulo C. Dias 2 Abstract The personal well-being index—school children (PWI-SC) is designed as a cross-cultural instrument to measure subjective well-being among high school–aged children. Several published cross-cultural studies have con- firmed adequate psychometric performance in terms of reliability, validity, and measurement invariance. This study adds to this literature by applying the Rasch approach to estimate invariant comparison in a cross-cultural context, applied to both Australian and Portuguese high school students. Participants were an age- and gender-matched convenience sample of 1,040 adolescents (520 cases in each group, 51.54% male) who ranged in age from 12 to 18 years (M ¼ 14.25 years, SD ¼ 1.71 years). It is found that both Portuguese and Australian data fit the Rasch measurement model, with excellent levels of reliability at a country level. However, when all of the data were combined, a slight misfit was found. This was resolved by removing some issues with item thresholds in standard of living among the 1 School of Psychology, Deakin University, Burwood, Victoria, Australia 2 Faculty of Philosophy, Catholic University of Portugal, Lisbon, Portugal Corresponding Author: Mark A. Stokes, School of Psychology, Deakin University, 221 Burwood Highway, Burwood, Victoria 3125, Australia. Email: mark.stokes@deakin.edu.au Evaluation & the Health Professions 1-22 ª The Author(s) 2019 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0163278718819219 journals.sagepub.com/home/ehp