Psychometric Properties of the Outpatient Physical Therapy Improvement in Movement Assessment Log (OPTIMAL) in Patients With Musculoskeletal Disorders: A Replication Study With Additional Findings

Abstract

The Outpatient Physical Therapy Improvement in Movement Assessment Log (OPTIMAL) is a recently developed self-report outcome instrument designed to measure the extent of activity limitation as defined by the World Health Organization. The purposes of the study were to replicate some aspects of the original study of the OPTIMAL Difficulty and Confidence scales and to conduct additional psychometric tests. A cross-sectional design was used in the study. Of a total of 1,150 patients who received treatment at 4 outpatient centers over the study period, 1,030 patients were recruited for this study and completed the OPTIMAL instrument and previously validated region-specific functional status measures. A variety of analytic methods were used to examine the extent of redundancy between the OPTIMAL Difficulty and Confidence scales, as well as the internal consistency reliability, standard error of measurement, known-groups validity, and convergent validity of OPTIMAL Difficulty Scale scores. The OPTIMAL Difficulty and Confidence scale scores were found in a factor analysis to be load-based on anatomical region rather than on difficulty and confidence concepts. Internal consistency reliability for the subscales of the Confidence Scale varied and was .80 or higher for the lower-extremity subscale but .50 or less for the trunk and upper-extremity subscales. Only cross-sectional relationships were examined, and another pure measure of activity limitation was not used for comparison. The findings generally did not support the psychometric properties of the OPTIMAL instrument. Although not conclusive, the data suggested that the OPTIMAL Difficulty and Confidence scales demonstrate substantial overlap. Reliability was generally low, with the exception of the lower-extremity subscale. Scores for the subscales of the Difficulty Scale differentiated among patients with lower-extremity versus trunk or upper-extremity diagnoses, but associations with previously validated region-specific measures were generally weak or absent. Clinicians treating outpatients with musculoskeletal disorders should consider alternative measures when attempting to quantify the extent of activity limitations.