Background: 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).
Aim: To generate and validate a parsimonious core set of ICF (PCSI) for LBP based on the IRT modelling.
Design: A cross-sectional study.
Setting: Nine hospitals in Jiangsu Province, China.
Population: We recruited patients with LBP.
Methods: 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.
Results: 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.
Conclusions: 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.
Clinical rehabilitation impact: 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.