PHYS THER
Vol. 81, No. 3, March 2001, p. 914
Author Response
Karl M Hermann, PT, PhD and
C Shane Reese, PhD
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Introduction
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We would like to thank Dr Jette for his thoughtful commentary on our study, and we appreciate the opportunity to respond. It is through dialogue such as this that the science and practice of physical therapy can be advanced. Important points were raised regarding our statistical approach and choice of measures used.
Our primary goal was to determine the relationships among 3 sets of variables (impairment measures, functional limitation measures, and disability measures) in patients with cervical spine disorders. Our objective was to look at these variables in a multivariate sense and not simply examine pair-wise comparisons. Dr Jette is correct in pointing out that canonical correlations test the strength of linear associations among sets of variables. A statistical approach that tests for nonlinear associations among sets of variables would be difficult due to the multivariate nature of the problem. Testing for nonlinear (eg, curvilinear) relationships is more easily done using univariate correlations, where nonlinearities are more straightforwardly addressed. Linearity is always a simplification of the truth, but often a fairly good one. Our multivariate approach, although linear, may yield insights that would not otherwise be found using univariate correlations. However, we agree with Dr Jette that other statistical approaches should be used to further elucidate the nature of relationships among disablement concepts, especially in light of recent findings.1,2 We also agree that determination of clinical thresholds from such studies could greatly affect practice.
We chose the measures used in this investigation because they are commonly used in daily practice and they have been studied previously. Dr Jette raises a very important issue in that many commonly used clinical measures purported to represent a single disablement concept actually represent more than one concept, thus making their interpretation problematic. We recognize that some of the measures we used (eg, Neck Disability Index) do not reflect distinct disablement concepts and that there is some overlap. The reader should be mindful of this as the results of our investigation are considered. We, too, believe that more valid measures representing clear and distinct disablement concepts must be developed in order for the science and practice of physical therapy to be advanced.
It is our hope that this investigation will stimulate further research and testing of clinical hypotheses as well as development of valid clinical measures that, as Dr Jette mentioned, will build a more solid foundation of evidence-based practice.
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References
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- Ferrucci L, Guralnik JM, Buchner D, et al. Departures from linearity in the relationship between measures of muscular strength and physical performance of the lower extremities: the Women's Health and Aging Study.
J Gerontol A Biol Sci Med Sci.1997; 52:M275–M285.[Abstract]
- Jette AM, Assmann SF, Rooks D, et al. Interrelationships among disablement concepts.
J Gerontol A Biol Sci Med Sci.1998; 53:M395–M404.[Abstract]
Copyright © 2001 by the American Physical Therapy Association.
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