Appendix 2.

Development and Testing of a Modified Clinical Disease Activity Index

One practice had information on three of four aspects of the CDAI – tender joint count (TJC), swollen joint count (SWJ) and physician global (PG). We developed two modifications of the CDAI using de-identified data supplied by John Cush, MD. These data contained all components of the CDAI. The two modifications are described below. We tested each modification against the original CDAI using a multi-level Kappa test. Both modifications performed well, but modification 2 was slightly better and was used to categorize patients from the one practice with only three elements of the CDAI.

	Description of calculation	Weighted kappa (95% confidence interval)	P-value
Modified CDAI 1	TJC+SWJ+ (PGx2)	0.80 (0.75 – 0.85	0.03
Modified CDAI 2	(TJC + SWJ + PG) x76/66	0.91 (0.87 – 0.95)	0.02