The purpose of this study was to evaluate the methods currently available to measure the functional outcomes of physiotherapy treatment for low back problems. As a preliminary step, all extant questionnaires were located and evaluated against practical criteria to determine their likely utility in clinical practice. This process identified a large number of questionnaires, however, only six back-specific questionnaires fulfilled the practical criteria for clinical application. Four of these questionnaires were selected for further evaluation along with a generic health status assessment instrument, the SF-36 Health Survey. Current recommendations suggest that a low-back specific and a generic questionnaire are required for comprehensive assessment of the impact of low back problems. The four back-specific questionnaires selected were the Oswestry Disability Questionnaire, the Quebec Back Pain Disability Scale, the Roland-Morris Disability Questionnaire and the Waddell Disability Index. An evaluation of the literature on the clinimetric properties of these questionnaires revealed that little information was available for the Quebec and Waddell questionnaires and no information was available for any of the questionnaires for a clinical population of people with low back pain seeking physiotherapy treatment in an Australian setting. The primary aim of the research was identify which, if any, of the questionnaires should be recommended for measuring outcomes of physiotherapy treatment for low back pain. Consecutive ambulatory (non-admitted) patients presenting for physiotherapy treatment at three public hospital physiotherapy outpatient departments, three community health services, and four private practices were invited to enter the study. Patients were included if they were seeking treatment for a low back problem, were aged 18 or over, and could read and write English. Subjects completed the questionnaires on two occasions six-weeks apart. One hundred and forty subjects returned the first set of questionnaires, and 106 the second set. The mean age of the sample at pre-test was 51 (SD 17) and ranged from 18 to 89 years. Sixty-six percent were female, 41% were employed and 12% were receiving compensation for their back problem. Duration of the back complaint was more than six weeks for 56% of subjects, and 60% reported five or more previous episodes or continuous pain. Referred pain in the buttock thigh or leg was reported by 70% of subjects. The first aim was to compare the questionnaires for acceptability and comprehensibility. Data quality was high for all the questionnaires (less than 5% missing data). As expected, subjects found the more complex SF-36 Health Survey more difficult to complete than three of the low-back questionnaires. However, less than 10% of subjects found any of the questionnaires more than a little difficult to complete. The next aim was to explore the internal structure and inter-relationships of the low-back questionnaires and the three physical scales of the SF-36 Health Survey (Physical Functioning, Role-Physical and Bodily Pain). Analysis of item-item correlation, item-total correlation and Cronbach�s alpha confirmed that all scales were internally consistent. Factor analysis confirmed item homogeneity (unidimensionality) of all questionnaires except the Roland-Morris Disability Questionnaire. The questionnaires were significantly intercorrelated, but correlations exceeded .70 only for the Oswestry, Quebec and Waddell questionnaires. The next aim of the research was to compare test-retest reliability of the questionnaires. The Oswestry, Quebec and SF-36 Physical Functioning scale had sufficient reliability and scale width for clinical application. Despite previous reports of high reliability, the Roland-Morris scale was significantly less reliable than several of the other questionnaires. This indicates the importance of establishing the measurement properties of a test in the population or setting in which it will be used. The Waddell Disability Index, and the SF-36 Role-Physical and Bodily Pain scales had insufficient scale width to be useful in clinical practice. More than 15% of respondents had an initial score on these scales that would not allow change to be detected with 90% confidence. The next aim of the research was to compare the responsiveness of the questionnaires. None of the questionnaires was consistently identified as more or less responsive than the others although two methods (effect size and Liang�s standardized response mean) suggested the SF-36 Bodily Pain scale was more responsive than some other questionnaires. A secondary aim of this section was to evaluate the validity of the many available responsiveness indices and a novel �reliable change� method. A �known groups� strategy was used to determine whether the responsiveness index could discriminate between the low-back relevant questionnaires and the SF-36 General Health scale, the scores of which did not change across the retest period. With the exception of the novel �reliable change� method the responsiveness indices were all found to be valid indicators of responsiveness. Guyatt�s Responsiveness Index, effect size and Liang�s standardized response mean discriminated at 95% confidence between the reference scale and all the low-back questionnaires. The standardized response mean, t-test, correlation and ROC methods discriminated between the reference scale and five or six of the seven other questionnaires. Guyatt�s index was recommended as the best of the criterion-based methods, and the effect size the best of the distribution-based methods. The three questionnaires identified as having sufficient reliability and scale width, the Oswestry, Quebec and SF-36 Physical Functioning scale, were next analysed for data fit to a Rasch model. All three questionnaires had good data fit and item function was not affected by time, age, gender or whether or not subjects reported avoiding bending. The final aim of this research was to identify by Rasch analysis items to supplement the SF-36 Physical Functioning scale. The new scale, named the Low-Back SF-36 Physical Functioning18, showed comparable reliability and responsiveness to the SF-36 Physical Functioning scale. Further research is required to establish the measurement properties of the Low-Back SF-36 Physical Functioning18 scale in an independent sample. However, it has the potential to improve the clinical measurement of function by providing clinicians with a single measurement tool for comprehensive assessment of patients with low back pain.
| Identifer | oai:union.ndltd.org:ADTP/235980 |
| Date | January 2003 |
| Creators | Davidson, Megan, m.davidson@latrobe.edu.au |
| Publisher | La Trobe University. School of Physiotherapy |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.latrobe.edu.au/copyright/disclaimer.html), Copyright Megan Davidson |
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