Lumbar computerized adaptive test and Modified Oswestry Low Back Pain Disability Questionnaire: relative validity and important change.

STUDY DESIGN: Retrospective analysis of longitudinal, observational cohort data. OBJECTIVES: To compare discriminating ability and minimal clinically important improvement (MCII) calculated using functional status (FS) measures estimated from the lumbar computerized adaptive test (LCAT) and Modified Oswestry Low Back Pain Disability Questionnaire (ODQ). BACKGROUND: The LCAT and ODQ are commonly used to estimate FS in patients seeking outpatient therapy but have not been compared directly. METHODS: Data from 8198 adult patients who completed the LCAT and ODQ at intake were analyzed, 3379 (41%) of whom completed both surveys at discharge. Global ratings of change data were available for 980 patients. Discriminating ability of FS estimates from the LCAT and ODQ was estimated using relative validity, calculated by dividing F values from LCAT and ODQ analyses of covariance for important risk-adjustment variables. MCII was estimated using receiver-operating-characteristic analyses by quartiles of intake FS values, and areas under the curves were compared. RESULTS: Relative validity ratios favored the LCAT for age (3.7; 95% confidence interval [CI]: 2.0, 8.9), acuity (1.3; 95% CI: 1.1, 1.6), comorbidities (1.8; 95% CI: 1.3, 2.6), and surgical history (1.8; 95% CI: 1.2, 2.9). MCII cut scores per quartile favored the LCAT. Receiver-operating-characteristic areas under the curves were not different. CONCLUSION: FS measures estimated by both questionnaires had similar psychometric characteristics. The LCAT FS estimates tended to be more discriminating than ODQ FS estimates. MCII cut scores by quartile of intake FS favored the LCAT. Given the need to be efficient and precise in estimating measures of FS, particularly in older patients, results favor the LCAT in busy, automated outpatient therapy clinics, which are increasingly serving an aging population.