Prospective judgments of acceptable outcomes for pain, interference and activity: Patient-determined outcome criteria.

The selection of outcome criteria for chronic pain, both the domain of measurement and the magnitude of change, in RCTs is largely determined by the investigators. The present study investigated patient-determined criteria for the magnitude of change necessary to achieve an 'acceptable outcome' (endpoint) on the brief pain inventory and two subscales of the multidimensional pain inventory. Seventy-eight patients attending a chronic pain out-patient clinic were asked to rate their current state on the measures and then complete the scales as they would if treatment were to result in an acceptable outcome. The differences between the two sets of scores are described in terms of raw change scores, percentage change and by comparing the judgments of acceptable outcomes to statistically defined criteria (reliable change index and clinically significant change). Participants indicated a lower level of pain severity, impact and interference and a higher level of activity as part of an acceptable outcome. The degree of acceptable changes indicated by participants was higher (median values=44-75%) than the 30-50% typically reported as the threshold for clinically significant change for measures of pain experience in other studies. We also conducted tests of two models of change judgment. Neither adequately fit the data. There were discrepancies between the patients' judgments of acceptable outcomes and the RCI and SCS criteria. Suggestions for future research and possible clinical implications are discussed.