A measuring standard created by the American College of Rheumatology (ACR). The "20" stands for 20% or greater reduction in the number of tender/painful and swollen joints as well as an improvement of 20% or more in at least three of the following measures:

• Physician assessed overall health and progress information
• Patient assessed overall health and progress information
• Pain scale
• Physical function (measured by the Health Assessment Questionnaire Disability Index, known as HAQ-DI)
• Lab test results that measure the amount of inflammation in joints