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Reliability and validity of the back performance scale: observing activity limitation in patients with back pain
Liv Magnussen1, Liv I Strand, Hildegunn Lygren
1Department of Public Health and Primary Health Care, Section of Physiotherapy Science, Faculty of Medicine, University of Bergen, Bergen, Norway. Liv.Magnussen@psybp.uib.no
Study Design:
A single group design to examine reliability and validity of the Back Performance Scale.
Objectives:
To examine intertester reliability, test-retest reliability, and concurrent validity of the Back Performance Scale.
Summary Of Background Data:
The Back Performance Scale is a condition-specific performance measure of activity limitation in patients with back pain. It includes five tests of daily activities requiring mobility of the trunk: sock test, pick-up test, roll-up test, fingertip-to-floor test, and lift test. Discriminative ability and responsiveness to important change have previously been demonstrated.
Methods:
A total of 41 patients with back pain participated in the study. Two physiotherapists examined test performances concurrently, but independently. The patients filled in three questionnaires, two reflecting perceived disability (Der Funktionsfragenbogen Hannover, Roland-Morris Disability Questionnaire) as well as one for fear avoidance of daily activities and work (Fear Avoidance Belief Questionnaire). One physiotherapist retested the patients after 2 to 3 days.
Results:
Intertester agreement of the Back Performance Scale sum score was very high (intraclass correlation coefficient 2.1): 0.996. Within-patient standard deviation (sw) on the 16-point Back Performance Scale was very low: 0.25. Test-retest reliability was high (intraclass correlation coefficient = 0.91, sw = 1.3). Intertester agreement of the separate tests was also very high, ranging from kappa= 0.90-1.00. Test-retest reliability was moderate to high (kappa= 0.55-0.83). A high correlation was demonstrated between the Back Performance Scale and the Der Funktionsfragenbogen Hannover: Spearman rho (rho) = 0.825, P < 0.01. Correlation between the Back Performance Scale and Roland-Morris Disability Questionnaire was moderate: rho = 0.454, P < 0.01. No correlation was demonstrated between the Back Performance Scale and the Fear Avoidance Belief Questionnaire.
Conclusion:
The Back Performance Scale appears to be a reliable and valid outcome measure of activity limitation.
