Study design: A reliability study was performed.
Objectives: To evaluate the test-retest reliability of self-reported functional status and pain in chronic low back pain patients by postal questionnaires.
Summary of background data: Evaluation tools focusing on the patients' self-reported physical function are recommended in studies on low back pain. Postal questionnaires are inexpensive and should be considered to assess long-term results. The reliability of a postal questionnaire has not been assessed in patients with chronic low back pain.
Methods: Forty-two patients with chronic low back pain (15 men, 27 women; mean age, 40 years; range, 20-61 years) agreed to participate in the study. The mean duration of symptoms was 8.9 years (range, 1-40 years). A postal questionnaire was sent to the patients twice within a 2-week interval. The questionnaire included the following items: work, back satisfaction, General Function Score (GFS), Oswestry Disability Index (ODI), pain, fear-avoidance beliefs, life satisfaction and pain medication.
Results: Thirty-seven patients (88%) returned both questionnaires. Except for lumbar pain, there were no statistical differences between the answers from the two questionnaires. The intraclass coefficient values ranged from 0.70 (lumbar pain) to 0.94 (ODI). The repeatability or absolute size of measurement error was 11.9 for the ODI and 28.6 and 34.2 for lumbar and leg pain, respectively. The kappa values for work, back satisfaction, and pain medication were 0.94 and 0.61, 0.62, and 0.64, respectively. The kappa values for the separate items in the GFS ranged from 0.41 to 0.79. The correlations between ODI and the GFS, lumbar pain, life satisfaction, and back satisfaction were 0.35, -0.72, -0.76, and 0.76, respectively.
Conclusion: The ODI was highly reliable. The questions about work, back satisfaction, and pain medication showed good agreement. The GFS, pain intensity, fear-avoidance beliefs, and life satisfaction appeared to lack sufficient reliability to be recommended in postal questionnaires.