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Responsiveness and Interpretability of the Portuguese Version of the Quebec Back Pain Disability Scale in Patients With Chronic Low Back Pain

Vieira, Ana C. MSc (Phys)*; Moniz, Sara MSc (Phys); Fernandes, Rita MSc (Phys); Carnide, Filomena PhD§; Cruz, Eduardo Brazete PhD

doi: 10.1097/BRS.0000000000000159
Health Services Research

Study Design. A prospective cohort study with a 6-week follow-up of patients with chronic low back pain undergoing physiotherapy.

Objective. To examine the responsiveness of the Portuguese version of the Quebec Back Pain Disability Scale (QBPDS-PT), and to determine the minimal clinically important difference, minimal detectable change (MDC), and floor/ceiling effects.

Summary of Background Data. Measuring change over time is critical to assess the effectiveness of a physiotherapy intervention or to distinguish individual differences in response to treatment.

Methods. One hundred thirty-two patients were recruited from 16 outpatient clinics in 7 different regions of Portugal. A final sample of 120 patients completed the QBPDS-PT twice: at the baseline and after 6 weeks of physiotherapy treatment. The patient global impression of change scale was used as an external criterion measure to distinguish between improved or nonimproved patients' scores between baseline and follow-up. The responsiveness of the QBPDS-PT was assessed through correlation coefficient and receiver operating characteristics curves. The minimal clinically important difference was estimated by the receiver operating characteristics curve method and the MDC through the standard error of measurement.

Results. The scale revealed moderate responsiveness (ρ = 0.426 and area under the curve = 0.741; 95% confidence interval: 0.645–0.837). The MDC achieved 19 points, whereas the minimal clinically important difference was found to be 6.5 points (area under the curve = 0.741, sensitivity = 72%, specificity = 71%). A floor effect was founded with 15.8% of the participants reporting values within the MDC at the lower end of the available range of scores. For the highest baseline scores of QBPDS-PT (≥34 points) the optimal cutoff point was found to be 10.5 points (area under the curve = 0.738, sensitivity = 73%, specificity = 67%).

Conclusion. The QBPDS-PT demonstrated moderate levels of responsiveness, and is recommended to measure change in disability in patients with chronic low back pain after physiotherapy intervention.

Level of Evidence: N/A

This study examined the responsiveness and interpretability of the Portuguese version of the Quebec Back Pain Disability Scale. The minimal detectable change achieved 19 points, whereas the minimal clinical important difference was found to be 6.5 points. The baseline functional disability scores influenced the optimal cutoff points identified.

*Serviço de Medicina Física e de Reabilitação do SESARAM, E.P.E. Madeira, Portugal

Centro de Medicina e Reabilitação, Reafi, Parede, Lisbon, Portugal

Escola Superior de Saúde, Instituto Politécnico de Setúbal, Portugal; and

§Universidade Técnica de Lisboa, Faculdade de Motricidade Humana, CIPER, LBMF, Lisboa, Portugal.

Address correspondence and reprint requests to Eduardo Brazete Cruz, PhD, Escola Superior de Saúde, Campus do Instituto Politécnico de Setúbal, Estefanilha, Edifício ESCE. 2914-503 Setúbal, Portugal; E-mail:

Acknowledgment date: July 26, 2013. Revision date: October 29, 2013. Acceptance date: November 26, 2013.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

No relevant financial activities outside the submitted work.

© 2014 by Lippincott Williams & Wilkins