Relative utility of a visual analogue scale vs a six-point Likert scale in the measurement of global subject outcome in patients with low back pain receiving physiotherapy

Background: Patients' subjective impression of change is an important construct to measure following physiotherapy, but little evidence exists about the best type of measure to use. Objective: To compare the construct validity and utility of two forms of a global subjective outcome scale (GSOS) in patients with back pain: Likert and visual analogue scale (VAS) GSOS. Design: Two samples of patients attending physiotherapy for back pain completed a questionnaire battery at discharge from physiotherapy including either a Likert or VAS GSOS. Participants: One hundred and eighty-seven {79 males, mean age 52.1 [standard deviation (SD) 15.5] years} patients completed the Likert GSOS and a separate sample of 144 patients [62 males, mean age 55.7 (SD 15.9) years] completed the VAS GSOS upon discharge from physiotherapy. Main comparisons: The two versions of the GSOS were compared using pre- and post-treatment changes in scores using a VAS (pain), Roland-Morris Disability Questionnaire (18-item version) and catastrophising subscale of the Coping Strategies Questionnaire 24. Results: Both versions of the GSOS showed significant (. P<. 0.01) moderate correlations (. r between 0.30 and 0.46) with changes in pain and disability. The correlations between the two types of GSOS and changes in catastrophising were trivial and not significant (Likert GSOS: r=. 0.07, P=. 0.372; VAS GSOS: r=. 0.10, P=. 0.267). There were fewer missing values in the Likert GSOS (1%) compared with the VAS GSOS (8%). Conclusions: The two versions of the GSOS showed similar validity; however, use of the Likert GSOS is recommended because of its greater utility.