Measurement properties of the sedentary behavior questionnaire in patients with chronic nonspecific low back pain.

INTRODUCTION The Sedentary Behavior Questionnaire (SBQ) is a brief and easy instrument to measure time spent on sedentary activities; however, no study has investigated the reliability and validity of this questionnaire in people with chronic low back pain (LBP). OBJECTIVE To investigate the internal consistency, test-retest reliability, measurement error, construct validity and interpretability of the SBQ against data derived from an accelerometer in patients with non-specific chronic LBP. STUDY DESIGN Cross-sectional study. SETTING Outpatient physiotherapy clinic. PATIENTS Seventy-five patients aged between 18 and 60 years (mean age of 42 years old) with non-specific chronic LBP were recruited for this study. INTERVENTIONS Not applicable. METHODS The Cronbach's α was calculated to investigate the internal consistency of the SBQ and the Intraclass Correlation Coefficient (ICC) was calculated to investigate the reliability of the SBQ between two administrations separated by a one-week interval. Measurement error was assessed calculating the SE of measurement (SEM) and minimal detectable change (MDC). Spearman correlation (r) was calculated to investigate the construct validity using hypothesis testing. Interpretability was investigated using ceiling and floor effects. RESULTS The Cronbach's α of the SBQ total score was 0.92, indicating homogeneity among the items of the instrument. The reliability of the SBQ was excellent (ICC > 0.75), without any evidence of ceiling and floor effects. Regarding measurement error, the total score of the SBQ showed a SEM and MDC of 109.8 minutes per day and 304.4 minutes per day, respectively. However, there were no correlations of the SBQ domains or the total score with the accelerometer-measured sedentary time (r < 0.25). CONCLUSION The SBQ is a reliable tool for quantifying time spent in sedentary activities of patients with chronic LBP. The SBQ showed poor construct validity compared to the accelerometer-measured sedentary time which indicates that patients may underestimate their time spent in sedentary activities.