Measurement of acute nonspecific low back pain perception in primary care physical therapy: reliability and validity of the brief illness perception questionnaire

BACKGROUND The eight-item Brief Illness Perception Questionnaire is used as a screening instrument in physical therapy to assess mental defeat in patients with acute low back pain, besides patient perception might determine the course and risk for chronic low back pain. However, the psychometric properties of the Brief Illness Perception Questionnaire in common musculoskeletal disorders like acute low back pain have not been adequately studied. Patients' perceptions vary across different populations and affect coping styles. Thus, our aim was to determine the internal consistency, test-retest reliability and validity of the Dutch language version of the Brief Illness Perception Questionnaire in acute non-specific low back pain patients in primary care physical therapy. METHODS A non-experimental cross-sectional study with two measurements was performed. Eighty-four acute low back pain patients, in multidisciplinary health care center in Dutch primary care with a sample mean (SD) age of 42 (12) years, participated in the study. Internal consistency (Cronbach's α) and test-retest procedures (Intraclass Correlation Coefficients and limits of agreement) were evaluated at a one-week interval. The concurrent validity of the Brief Illness Perception Questionnaire was examined by using the Mental Health Component of the Short Form 36 Health Survey. RESULTS The Cronbach's α for internal consistency was 0.73 (95% CI, 0.67 - 0.83); and the Intraclass Correlation Coefficient test-retest reliability was acceptable: 0.72 (95% CI, 0.53 - 0.82), however, the limits of agreement were large. The Intraclass Correlation Coefficient measuring concurrent validity 0.65 (95% CI, 0.46 - 0.80). CONCLUSION The Dutch version of the Brief Illness Perception Questionnaire is an appropriate instrument for measuring patients' perceptions in acute low back pain patients, showing acceptable internal consistency and reliability. Concurrent validity is adequate, however, the instrument may be unsuitable for detecting changes in low back pain perception over time.