Single vs composite measures of pain intensity: relative sensitivity for detecting treatment effects.

Assay sensitivity remains a significant issue in pain clinical trials. One possible method for increasing assay sensitivity for detecting changes in pain intensity is to increase the reliability of pain intensity assessment by increasing the number of intensity ratings obtained, and combining these ratings into composite scores. The current study performed secondary analyses from a published clinical trial to test this possibility. The reliability and assay sensitivity pain intensity scores made up of 1 to 9 24-hour pain intensity recall ratings were compared. Although the reliability of the outcome measures improved as the number of items increased, this increase in reliability was not associated with an increase in assay sensitivity. A single 24-hour recall rating was about as valid (sensitive) for detecting treatment effects as composite scores made up of 2 to 9 different ratings. If this finding replicates in other pain populations, it has significant implications for the design and conduct of pain clinical trials. Specifically, it suggests the possibility that assessment burden (and associated costs and problems related to missing data) might be greatly reduced by specifying a single recall rating as the primary outcome variable. Research is needed to explore this possibility further.