Table 2.

Demographic and serological characteristics of the study population.

Characteristic	First-degree Relatives, n = 306	NAN Controls, n = 323	White Controls, n = 293
Female, %	68.6	62.2	63.5
Age, yrs ± SD	35 ± 13^*	33 ± 11	43 ± 13^**
Urban, %	53.3	58.4	82.6^**
Education level, yrs, mean ± SD	11.0 ± 2.7^*	9.2 ± 2.1	13.8 ± 1.6^**
Anti-CCP2-positive; ≥ 40 units, %	8.5 (22/258)^*	3.6 (7/192)	0 (0/147)^**
RF-positive; ≥ 50 units, %	33.3 (86/258)^*	7.3 (14/192)	4.1 (6/147)^**
RF- and anti-CCP2-positive, %	3.1 (8/258)	1.6 (3/192)	0 (0/147)^**

↵* p < 0.05 FDR versus NAN controls;
↵** p < 0.01 white controls versus FDR and NAN controls. CCP: cyclic citrullinated peptide; RF: rheumatoid factor; FDR: first-degree relative; NAN: North American Native.