Published Papers - Abstract 1004

Cordier R, Brown T, Clemson L & Byles J. Evaluating the Longitudinal Item and Category Stability of the SF-36 Full and Summary Scales Using Rasch Analysis BioMed Research International, 2018; :

The Medical Outcome Study Short Form 36 (SF-36) is widely used for measuring Health-Related Quality of Life (HRQoL) and has undergone rigorous psychometric evaluation using Classic TestTheory (CTT).However, Item Response Theorybased evaluation of the SF-36 has been limited with an overwhelming focus on individual scales and cross-sectional data. Purpose. This study aimed to examine the longitudinal item and category stability of the SF-36 using Rasch analysis. Method. Using datafrom the 1921-1926 cohort of the Australian Longitudinal Study onWomen’s Health, responses of the SF-36 from six waves of data collection were analysed. Rasch analysis using Winsteps version 3.92.0 was performed on all 36 items of the SF-36 and items that constitute the physical health and mental health scales. Results. Rasch analysis revealed issues with the SF-36 not detected using classical methods. Redundancy was seen for items on the total measure and both scales across all waves of data. Person separation indexes indicate that the measure lacks sensitivity to discriminate between high and low performances in this sample.The presence of Differential Item Functioning suggests that responses to itemswere influenced by locality andmarital status. Conclusion. Previous evaluations of the SF-36 have relied on cross-sectional data; however, the findings of the current study demonstrate the longitudinal efficacy of the measure. Application of the Rasch Measurement Model indicated issues with internal consistency, generalisability, and sensitivity when the measure was evaluated as a whole and as both physical and mental health summary scales. Implications for future research are discussed.

Open Access Article