Emotional vitality in caregivers: Application of Rasch Measurement Theory with secondary data to development and test a new measure

Objective: To describe the practical steps in identifying items and evaluating scoring strategies for a new measure of emotional vitality in informal caregivers of individuals who have experienced a significant health event. Design: The psychometric properties of responses to selected items from validated health-related quality of life and other psychosocial questionnaires administered four times over a one-year period were evaluated using Rasch Measurement Theory. Setting: Community. Subjects: A total of 409 individuals providing informal care at home to older adults who had experienced a recent stroke. Main measures: Rasch Measurement Theory was used to test the ordering of response option thresholds, fit, spread of the item locations, residual correlations, person separation index, and stability across time. Results: Based on a theoretical framework developed in earlier work, we identified 22 candidate items from a pool of relevant psychosocial measures available. Of these, additional evaluation resulted in 19 items that could be used to assess the five core domains. The overall model fit was reasonable (÷2 = 202.26, DF = 117, p = 0.06), stable across time, with borderline evidence of multidimensionality (10%). Items and people covered a continuum ranging from -3.7 to +2.7 logits, reflecting coverage of the measurement continuum, with a person separation index of 0.85. Mean fit of caregivers was lower than expected (-1.31 ±1.10 logits). Conclusion: Established methods from the Rasch Measurement Theory were applied to develop a prototype measure of emotional vitality that is acceptable, reliable, and can be used to obtain an interval level score for use in future research and clinical settings.