Reliability, responsiveness and minimal clinically important difference of the two Fear Avoidance and Beliefs Questionnaire scales in Italian subjects with chronic low back pain undergoing multidisciplinary rehabilitation.

Background: The Fear-Avoidance Beliefs Questionnaire (FABQ) is a widely used outcome measure. There is still a lack of information concerning responsiveness and minimal clinically important difference (MCID), limiting its use for clinical and research purposes.

Aim: The aim of this study was to examine reliability, responsiveness and MCID of the two FABQ scales in subjects with chronic low back pain.

Design: Methodological research based on a prospective single-group observational study.

Setting: Outpatient, Unit of rehabilitation.

Population: Chronic non-specific low back pain.

Methods: At the beginning and the end of a multidisciplinary program (8-week), 129 subjects completed the FABQ scales. Reliability was determined as internal consistency (Cronbach's alpha) and test-retest reliability (96-hour interval; N.=64; Interclass correlation coefficient [ICC 2.1]). Responsiveness was calculated both by distribution-based and anchor-based methods, using as external criterion the Global Perceived Effect Scale (GPE: 7 levels), rated by each individual.

Results: Cronbach's alpha and ICC(2,1) were respectively: 0.75 and 0.90 for FABQ-Physical Activity Scale (FABQ-PA), and 0.85 and 0.95 for FABQ-Work Scale (FABQ-W). Minimum detectable change (MDC95) values were 3.69 points for FABQ-PA, and 5.95 points for FABQ-W. In receiver-operating characteristic curves, splitting GPE data into null/minimal/moderate improvement vs. large improvement (GPE 0-2 vs. GPE 3): 1) for FABQ-PA, the area under the curve (AUC) was 0.97 and the best cutoff score identifying meaningful change in fear-avoidance beliefs about physical activity was a change of 4 points; 2) for FABQ-W, the AUC was 0.97 and the best cutoff score for meaningful change in fear-avoidance beliefs about work activities was a change of 7 points.

Conclusions: After triangulation of the above results, a change of 4 points for FABQ-PA and 7 points for FABQ-W were selected as MCID. These two values represent cutoffs that seem to accurately identify meaningful change in fear-avoidance beliefs, according to subject's judgement.

Clinical Rehabilitation Impact: The present study calculated - in a sample of people with chronic low back pain - the minimal clinically important change of the two FABQ scales (FABQ-Physical Activity Scale and FABQ-Work Scale). These values increase confidence in interpreting score changes, thus enhancing their meaningful use in both research and clinical contexts.