This study evaluated the psychometric properties of the Relative Mastery Scale (RMS). Valid and reliable client-centered instruments support practice in value-based health care and community-based settings. Participants were 368 community-dwelling adults aged 18 to 95 years. Researchers conducted validity and reliability examinations of the RMS using classical test theory and Rasch measurement model. A partial credit model allowed exploration of individual scale properties. Spearman's correlation coefficients between items were statistically significant at the .01 level. Cronbach's alpha coefficient was .94 showing strong internal consistency. In exploratory factor analysis, Factor 1 accounted for 71% of variance with an eigenvalue of 4.26. In Rasch analysis, the 5-point rating scale demonstrated adequate functioning, confirmed unidimensionality, and person/item separation. The RMS instrument demonstrates sound psychometric characteristics. A valid and reliable measure of internal occupational adaptation supports application to monitor progress of internal occupational adaptation across a variety of individuals.
Keywords: Rasch analysis; measurement; occupational adaptation; self-awareness; treatment effectiveness.