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

Abstract

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. 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. 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). 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.