Simplified functioning assessment for low back pain: ICF-based item response theory modelling.

Abstract

Despite the growing interest of the item response theory (IRT) in assessment of person abilities and functioning difficulties in screening tools, there is scarcity of research using IRT on ICF-based tools for persons with low back pain (LBP). To generate and validate a parsimonious core set of ICF (PCSI) for LBP based on the IRT modelling. A cross-sectional study. Nine hospitals in Jiangsu Province, China. We recruited patients with LBP. All participants completed the 78 items of the comprehensive ICF Core Set for LBP. The five-point scoring system was converted to dichotomous data with 1 as functioning/independent and 0 as impairment/dependent. Psychometric properties of the data were examined using Mokken Scale analysis and parametric item response modelling. This study recruited 306 participants (185 females and 121 males) with LBP. The overall median age of the study participants was 50.28 (95% CI 23.34; 82.05) years. We constructed a three-parameter logistic model with 28 ICF categories (8 of body function, 18 of activities and participation, and two of body structures). The internal consistency was good with Cronbach's alpha = 0.927 and latent class reliability coefficient (LCRC) = 0.955. The model was validated by significant correlations (P<0.001) of its estimated person abilities with the Oswestry Disability Index (ODI, r=-0.41), the Roland-Morris Disability Questionnaire (RMDQ, r=-0.57), the Physical Component Summary (PCS, r=0.63), and the Mental Component Summary (MCS, r = 0.46) of 12-Item Short Form Survey (SF-12). The person abilities and item difficulties were integrated into a Wright map that offered a background for making individualized clinical decisions. The PCSI of LBP with 28 categories has good construct validity and internal consistency, and is a convenient instrument for assessing functioning among persons with LBP. The IRT model provided theoretical and algorithmic support for deriving a simplified model for functioning assessment hence serving a basis for formulating rehabilitation plans in clinical practice and research. A parsimonious core set of ICF (PCSI) for LBP based on the IRT modelling provides a background for making individualized clinical decisions based on item difficulties.