The course of a single RA patient over the first 19 years of illness. Circles represent HAQ scores. For increased visibility, the insert provides HAQ scores on the appropriate scale. Note the wide-ranging variability of the HAQ scores. The AUC (triangles) provides smoothing that allows further analysis. The AUC represents the total burden of RA over time, and can be used to define functional disability as an outcome. The bi-directional arrow in the insert provides another method to define functional disability: a sustained level of disability over a defined time period. In this illustration disability is defined as an HAQ score of 2 or greater over a period of at least 2 years. See text for details. RA, rheumatoid arthritis; HAQ, Health Assessment Questionnaire; AUC, area under the curve.