Systematic review reveals heterogeneity in definition of a clinically relevant difference in pain

To describe the pain decrease considered as clinically relevant when designing a trial and reporting its results.

A systematic review of the literature in MEDLINE was conducted to select randomized controlled trials (RCTs) with pain as a primary outcome. Data extracted included the definition (terms and values) of a clinically relevant difference in pain, the type of pain studied (acute or chronic), the level of application (group or individual) of the clinically relevant difference, and the reference justifying the choice of value for clinically relevant difference.

Seventy-four trials were included, and only 16 articles justified the choice of a value for clinically relevant difference with a reference citation. The values chosen for the clinically relevant relative decrease in pain varied from 4 to 40 mm or from 15% to 55% at the group level and from 20 to 50 mm at the individual level. In seven articles, the authors confused the application of the reference value at the individual or group level.

Our review revealed a great heterogeneity in definition, format, and values of what is considered a clinically relevant difference in pain in RCTs of analgesics, and standardizations are advisable.