[Measuring disability of patients with low-back pain--validation of a German version of the Roland & Morris disability questionnaire].
BACKGROUND
In this study three instruments measuring disability of patients with low-back pain are presented and evaluated: (1) the Behinderungsfragebogen (RM) - a German version of the Roland & Morris disability questionnaire (RDQ) (2) a numerical rating scale measuring disability in general and (2) eight numerical rating scales measuring specific dimensions of disability (standing, sitting, walking, driving a car, carrying light loads, carrying heavy loads, sleeping, and sexual intercourse).


METHODS
The psychometric evaluation, including the item analysis, test reliability, test validity, and responsiveness of the instruments, is based on two samples. Sample A comprises 345 patients with low-back pain: 282 of these patients took part in the Swiss multicentre intervention study testing the effectiveness of in-patient rehabilitation of sub-chronic and chronic low-back pain under an integrative group treatment program. The instruments were administered at different times in the therapeutic process (t1: at hospital admission; t4: follow-up after one year). 63 patients were hospitalized (orthopedic or rheumatological units) for medical examinations (myelography or infiltration of facets) or rehabilitation of low-back pain. The instruments were administered twice within 24 h to measure test-retest correlation. In order to determine the psychometric parameters as accurately as possible, the two samples were examined jointly. Sample B is composed of 41 patients with low-back pain participating in the study "Prädiktoren des Erfolgs bei stabilisierenden Wirbelsäuleneingriffen" (Success predictors of effectiveness of surgical interventions for spinal stabilization).


RESULTS
All instruments proved to be generally reliable and valid (high or medium correlations with each other and with a German version of the Oswestry Disability Questionnaire) as well as responsive tools for measuring the momentary disability of patients with back pain. The psychometric examination of the test validity showed that patients' perceptions of their disability were influenced by their psychological well-being. The correlation between the 3 instruments and physical tests was low. The RM is not a homogeneous instrument. Factor analysis (principal component analysis, rotation Varimax) indicated 6 factors. Because of the small number of items for each factor it is not appropriate to treat RM in terms of dimensions of disability.


CONCLUSIONS
The RM is an instrument measuring patients' perception of their disability that offers simple, fast practicability for patients and tester. The 2 rating scales: The 8 numerical rating scales measuring specific dimensions of disability (QL3) offer all the advantages of the numerical rating scale measuring disability in general (QL1) (simple instruction, high plausibility for the patients, and simple, fast practicability), but they provide more information about the patient's disability, which allows comparisons of disability at different times in the therapeutic process. Numerical rating scales are not suitable for patients with poor ability to abstract. For these patients it is necessary to use a questionnaire which asks concretely about what the patient can or cannot do (e. g. RM). Because of its better psychometric properties, the QL3 should be favored over the RM.
Exner
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Psychiatrische Universitätspoliklinik, Kantonsspital, Basel.
Keel
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