On “Motor control exercise for chronic low back pain…” Costa LOP, Maher CG, Latimer J, et al. Phys Ther. 2009;89:1275–1286.

Abstract

In the interest of full disclosure, Dr Dennis Hart is a director of Focus on Therapeutic Outcomes, Inc (FOTO), which develops outcome measures and services for physical therapy and rehabilitation . The work by Costa et al1 represents a step forward in the assessment of treatments that are helpful for patients with lumbar spine impairments. The strength of their study lies in their design, which has been nicely reviewed by Fritz.2 However, we would like to direct attention to a psychometric matter that appears to have been overlooked by Fritz, the editors and reviewers, and the authors. Costa et al used the Patient-Specific Functional Scale (PSFS)3,4 to assess change in “activity” in their sample. Using aggregated PSFS scores to assess change in groups of patients represents a major conceptual and psychometric error, which makes interpretation of results difficult. In the present study, the authors also used the Roland-Morris Disability Questionnaire5 to assess “activity,” which provided results similar to those obtained using the aggregated PSFS scores, so our discussion is entirely related to the psychometric appropriateness of using aggregated PSFS scores to assess change in function in groups of patients, not the ultimate results of the study. If one starts with the assumption that the reported purpose of the PSFS is to assess functional ability and its change in …