Development and initial validation of the back pain functional scale

A prospective repeated-measures design was applied.

To examine the measurement properties of the Back Pain Functional Scale (BPFS) and the Roland-Morris Questionnaire (RMQ) and to formulate hypotheses and sample size estimates for a subsequent comparison study.

Although there are numerous functional status measures for patients with low back pain, most have been conceived of and validated with a group rather than an individual patient as the unit of interest. Also, little has been done to formally compare-this includes the generation of a priori hypotheses, followed by statistical hypotheses testing-the many competing measures.

Subjects were 77 patients with low back pain who were referred by physicians to 10 outpatient physical therapy clinics located in Canada and the United States. The questionnaires were administered at patients' initial visits, within 48 hours of the initial visit, and at 1-, 2-, and 3-week follow-up visits. Reliability, cross-sectional validity, and longitudinal validity (sensitivity to change) coefficients were calculated.

Test-retest reliability estimates of 0.81 and 0. 88 were obtained for the RMQ and BPFS, respectively. The measures demonstrated similar levels of cross-sectional validity. Correlations of 0.56 and 0.65 were noted between a prognostic rating of change and the RMQ and BPFS, respectively. The RMQ demonstrated a ceiling effect. Approximately 180 patients are needed for a subsequent head-to-head comparison study of the measures.

The BPFS appears to have sound measurement properties, and a formal head-to-head comparison study with the RMQ is warranted.