Implementation of the DC-ART category requires a quantitative definition of its descriptive components, the first of which is that such therapy "improve and sustain function." While function is generally taken to include physical, social, and emotional elements, a case is made for restricting function, in this context, to physical function. It is acknowledged that at present there are scanty data on which to determine the minimal size of improvement in function needed to satisfy DC-ART criteria and, in so doing, predict longer term benefit. Until more information is available on predictive data on patients with rheumatoid arthritis and natural course effects in healthy individuals, it is reasonable to use the arbitrary 25-50% improvements traditionally considered by clinicians to represent clinically important change.