Developing precise disability measures for back pain

Measurement of disability is crucial to many aspects of the rehabilitation process including capturing individual level changes, evaluating treatment effectiveness, and making policy decision, and administration costs. Many condition-specific self-reported instruments were developed over the past three decades to meet the need for assessment of disability resulting from back pain. However, these existing back pain disability measures have considerable limitations in terms of measurement precision and comprehensiveness. In order to overcome these limitations, precise measures should have the tremendous number of items either covering the wide range of ability traits or matching items to person ability closely. However, it is impossible to achieve the goals under the conventional classical test theory framework. Therefore, the aims of this study are to create precise disability measures with adequate measurement precision.;The study consisted of the following three steps to accomplish the goals; 1) investigating the item level psychometrics of the ICF Activity Measure will be determined by using Rasch analysis (one-parameter Item Response Theory model), 2) creating three short forms of the ICFAM based on the item level psychometrics, 3) comparison of three measures in terms of relative precision; the Computer Adaptive Testing (CAT) measure of the ICFAM, the three 10-item short form measures of the ICFAM, and the Oswestry Back Pain Disability Questionnaire (ODQ) measure as a most popular conventional back pain disability instrument.;Three constructs of the ICFAM and three 10-item short forms of the ICFAM were found to have a multidimensional construct. However, some findings still implicate the possibility of subconstructs of essentially unidimensional construct. The item difficulty hierarchical order did not reflect the hypothetical hierarchy based on the MET values except walking/moving construct. The empirical hierarchy fairly well follows either a clinical feature of back pain or motor control theory. The three IRT-based short forms with adequate breadth were created based on item-level psychometric properties. These were applied to 42 back pain and 42 non-back pain groups as well as the CAT of the ICFAM and the ODQ. The CAT outperformed the short forms and the ODQ except walking/moving construct, while the short forms outperformed the ODQ in terms of precision. The results may implicate that researchers/clinicians should be encouraged to use the CAT measure of the ICFAM, since it is precise and efficient measure. The IRT-based short forms of the ICFAM may be an alternative, when computer systems are not readily available.