The clinical importance of changes in the 0 to 10 numeric rating scale for worst,
least, and average pain intensity: analyses of data from clinical trials of
duloxetine in pain disorders.
Author(s): Farrar JT, Pritchett YL, Robinson M, Prakash A, Chappell A.
Affiliation(s): Department of Biostatistics and Epidemiology, University of Pennsylvania School
of Medicine, Philadelphia, PA19041, USA. jfarrar@mail.med.upenn.edu
Publication date & source: 2010, J Pain. , 11(2):109-18
Data on 1,700 patients pooled from 5 randomized, placebo-controlled duloxetine
studies (3 in diabetic peripheral neuropathic pain and 2 in fibromyalgia) were
analyzed to determine clinically important differences (CIDs) in the 0 to 10
Numeric Rating Scale-Pain Intensity (NRS-PI) for patient-reported "worst" and
"least" pain intensity while validating the previously published level for
"average" pain. The correspondence between the baseline-to-endpoint raw and
percentage change in the NRS-PI for the worst, least, and average pain were
compared to patients' perceived improvements at endpoint as measured by the
7-point Patient Global Impression of Improvement (PGI-I) scales. Stratification
by baseline pain separated the raw but not the percent change scores. The PGI-I
category of "much better" or above was our a priori definition of a CID. Cutoff
points for the NRS-PI change scores were determined using a receiver operator
curve analysis. A consistent relationship between the worst and average NRS-PI
percent change and the PGI-I was demonstrated regardless of the study, pain type,
age, sex, or treatment group with a reduction of approximately 34%. The least
pain item CID was slightly higher at 41%. Raw change CID cutoff points were
approximately -2, -2.5 and -3 for least, average, and worst pain respectively.
PERSPECTIVE: We determined an anchor-based value for the change in the worst,
least, and average pain intensity items of the Brief Pain Inventory that best
represents a clinically important difference. Our findings support a standard
definition of a clinically important difference in clinical trials of
chronic-pain therapies.
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