Evidence for measurement bias of the short form health survey based on sex and metropolitan influence zone in a secondary care population

Abstract

Background and objectives: The 12-item Short Form Health Survey (SF-12) is a widely used measure of health related quality of life, but has been criticized for lacking an empirically supported model and producing biased estimates of mental and physical health status for some groups. We explored a model of measurement with the SF-12 and explored evidence for measurement invariance of the SF-12. Research design and methods: The SF-12 was completed by 429 caregivers who accompanied patients with cognitive concerns to a memory clinic designed to service rural/remote-dwelling individuals. A multi-group confirmatory factor analysis was used to compare the theoretical measurement model to two empirically identified factor models reported previously in general population studies. Results: A model that allowed mental and physical health to correlate, and some items to cross-load provided the best fit to the data. Using that model, measurement invariance was then assessed across sex and metropolitan influence zone (MIZ; a standardized measure of degree of rurality). Discussion: Partial scalar invariance was demonstrated in both analyses. Differences by sex in latent item intercepts were found for items assessing feelings of energy and depression. Differences by MIZ in latent item intercepts were found for an item concerning how current health limits activities. Implications: The fitting model was one where the mental and physical health subscales were correlated, which is not provided in the scoring program offered by the publishers. Participants' sex and MIZ should be accounted for when comparing their factor scores on the SF-12. Additionally, consideration of geographic residence and associated cultural influences is recommended in future development and use of psychological measures with such populations.