Table 1. Baseline characteristics of RA patients in the cohort (2000–2008).

	RA cases (N = 1007)	Controls (N = 921,192)	p-value
Mean age (SD), years	57.76 ± 15.41	41.78 ± 20.32	< 0.0001
Female, %	76.3	48.9	< 0.0001
Clinic visits
No. of all visits	88,713	109,777,857
Mean no. per year	21.59 ± 15.72	14.10 ± 12.6	< 0.0001
Median no. per year	18	10.57
Diagnostic records
No. of all diagnostic records	141,394	163,043,706
Mean no. per year	34.51 ± 29.84	21.12 ± 22.80	< 0.0001
Median no. per year	26.31	13.87
Diagnostic codes (ICD-9-CM)
No. of diagnostic codes	2328	13,392
Mean no. per year	7.98 ± 4.93	4.19 ± 2.56	< 0.0001
Median no. per year	6.96	3.7