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      Clinical importance of changes in chronic pain intensity measured on an 11-point numerical pain rating scale :

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      Pain
      Elsevier BV

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          Abstract

          Pain intensity is frequently measured on an 11-point pain intensity numerical rating scale (PI-NRS), where 0=no pain and 10=worst possible pain. However, it is difficult to interpret the clinical importance of changes from baseline on this scale (such as a 1- or 2-point change). To date, there are no data driven estimates for clinically important differences in pain intensity scales used for chronic pain studies. We have estimated a clinically important difference on this scale by relating it to global assessments of change in multiple studies of chronic pain. Data on 2724 subjects from 10 recently completed placebo-controlled clinical trials of pregabalin in diabetic neuropathy, postherpetic neuralgia, chronic low back pain, fibromyalgia, and osteoarthritis were used. The studies had similar designs and measurement instruments, including the PI-NRS, collected in a daily diary, and the standard seven-point patient global impression of change (PGIC), collected at the endpoint. The changes in the PI-NRS from baseline to the endpoint were compared to the PGIC for each subject. Categories of "much improved" and "very much improved" were used as determinants of a clinically important difference and the relationship to the PI-NRS was explored using graphs, box plots, and sensitivity/specificity analyses. A consistent relationship between the change in PI-NRS and the PGIC was demonstrated regardless of study, disease type, age, sex, study result, or treatment group. On average, a reduction of approximately two points or a reduction of approximately 30% in the PI-NRS represented a clinically important difference. The relationship between percent change and the PGIC was also consistent regardless of baseline pain, while higher baseline scores required larger raw changes to represent a clinically important difference. The application of these results to future studies may provide a standard definition of clinically important improvement in clinical trials of chronic pain therapies. Use of a standard outcome across chronic pain studies would greatly enhance the comparability, validity, and clinical applicability of these studies.

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          Neglected topics in chronic pain treatment outcome studies: determination of success.

          Although literature on chronic pain treatment outcome has made substantial strides in improving the quality of the studies reported, there remain a number of factors that lead to qualification of the generally positive results. In the two previous papers in this series a set of migrating factors was discussed, namely, representativeness of the samples treated in these outcome studies, relapse, and non-compliance with therapeutic recommendations. Additional limitations include the lack of agreement on the criteria on which to base evaluation of the success of treatment outcome and the percentage of treated patients included in follow-up data. In this paper, the most common methods for determining success are described (group effects based on standard and quasi-standard outcome measures). The limitations of this approach are discussed and alternative strategies are presented that focus not only on traditional criteria based on group means but on additional criteria including: (a) importance of change (i.e., clinical vs. statistical significance), (b) proportion of patients who improve, (c) cost, (d) efficiency in treatment delivery, (e) and consumer acceptance and satisfaction.
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            Author and article information

            Journal
            Pain
            Pain
            Elsevier BV
            0304-3959
            2001
            November 2001
            : 94
            : 2
            : 149-158
            Article
            10.1016/S0304-3959(01)00349-9
            11690728
            4ecfccc4-cec6-4dee-92ea-dccec2369cff
            © 2001
            History

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