Assessing the Structural Validity and Measurement Invariance of the Whole Person Health Index

Background: The emergence of "whole person health" presents valuable opportunities for understanding and treating individuals as their complete selves. At the same time, holistic approaches to health introduce measurement challenges, highlighting the need for expansive yet manageable instruments to capture a broader concept of health. The Whole Person Health Index (WPHI) is a nine-item question set that asks respondents to rate their overall general health as well as their quality of life, social and family connections, diet, physical activity, stress, sleep, existential wellbeing, and ability to manage their health. It has been suggested for use in clinical settings and population surveys, and it has shown good promise in an initial evaluation study. Objective: The present study offers an exploratory look at the psychometric properties of the WPHI. Methods: The WPHI items were included on the 11th round of the National Center for Health Statistics Research and Development Survey (RANDS 11), conducted January-March 2025, which used samples of adults from commercially available survey panels. Descriptive and psychometric analyses were applied to explore the factor structure and functioning of the WPHI overall and across different population subgroups. Results: The WPHI demonstrated strong internal consistency and generally favorable measurement properties. Exploratory and confirmatory factor and bifactor analyses with split-half samples provided evidence that responses are largely driven by a dominant general factor, although model fit met some but not all conventional benchmarks for a strict single-factor model. Differential item functioning was detected for self-rated health by age, but not for other items or subgroups. Conclusion: Overall, the WPHI's subjective ratings appear to reflect a common underlying construct, supporting its utility as a broad measure of health and well-being consistent with the whole person health concept. Differences in item interpretation may suggest caution making direct comparisons of index scores across age groups.