The course of a single RA patient over 13 years of illness. Circles represent HAQ scores. Note the wide-ranging variability of the HAQ scores. Although it is difficult to give meaning to these HAQ scores or analyze them, 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. See text for details. RA, rheumatoid arthritis; HAQ, Health Assessment Questionnaire; AUC, area under the curve.