Measurement properties of the 12-item Short Form Health Survey version 2 in Australians with lung cancer: a Rasch analysis

Abstract

Background: The 12-item Short-Form Health Survey version 2 (SF-12v2), a widely used, generic patient-reported measure of health status that provides summary scores of physical and mental health. No study to date has examined the measurement properties of the SF-12v2 in patients with lung cancer using Rasch analysis. The aim of this study was to extend the psychometric evaluations of the SF-12 within the lung cancer population to ensure its validity and reliability to assess the health status in this population. Methods: Participants in the Victorian Lung Cancer Registry (VLCR) who completed the SF-12v2 between 2012 and 2016 were included in this study. The structural validity of the SF-12v2 was assessed using Rasch analysis. Overall fit to the Rasch measurement model was examined as well as five key measurement properties: uni-dimensionality, response thresholds, internal consistency, measurement invariance and targeting. Results: A total of 342 participants completed the SF-12v2 three months following their lung cancer diagnosis. The SF-12 Physical Component Score (PCS-12) did not fit the overall Rasch measurement model (χ2 107.0; p < 0.001). Three items deviated significantly from the Rasch model (item fit residual beyond ± 2.5) with signs of dependency between item responses and disordered thresholds. Nevertheless, the PCS-12 was uni-dimensional with good internal consistency (person separation index [PSI] 0.83) and reasonable targeting. In contrast, the SF-12 Mental Component Score (MCS-12) had good overall model fit (χ2 35.1; p = 0.07), reasonable targeting and good internal consistency (PSI 0.81). Conclusions: Rasch analysis suggests that there is general support for the reliability of the SF-12v2 as a measure of physical and mental health in people with lung cancer. However, the appropriateness of some items (e.g. pain) in the PCS-12 is questionable and further refinement of the scale including changing the response options may be required to improve the ability of the SF-12v2 to more appropriately assess the health status of this population.