Table 1.

Characteristics of RA cases and noncases among female spouses in the Agricultural Health Study, 1993–2010.

Characteristic	Comparison n = 24,018 n (%)	All RA cases		Incident cases
		Case n = 275 n (%)	OR (95% CI)	Case n = 132 n (%)	OR (95% CI)
Age at enrollment
< 40 years old	7,548 (31)	35 (13)	1.0 (referent)	21 (16)	1.0 (referent)
40–49 years old	7,178 (30)	65 (24)	2.0 (1.3, 2.9)	37 (28)	1.9 (1.1, 3.2)
50–59 years old	5,726 (24)	107 (39)	4.0 (2.7, 5.9)	47 (36)	2.8 (1.8, 4.9)
≥ 60 years old	3,566 (15)	68 (25)	4.1 (2.7, 6.2)	27 (20)	2.9 (1.5, 4.8)
State
North Carolina	6,929 (29)	105 (38)	1.0 (referent)	46 (35)	1.0 (referent)
Iowa	17,089 (71)	170 (62)	0.75 (0.58, 0.96)	86 (65)	0.83 (0.58, 1.2)
Race
White	23,089 (98)	262 (97)	1.0 (referent)	128 (98)	1.0 (referent)
Nonwhite	523 (2)	9 (3)	1.4 (0.71, 2.7)	2 (2)	0.67 (0.16, 2.7)
Education
≤ High school	9,155 (43)	119 (49)	1.0 (referent)	50 (43)	1.0 (referent)
> High school	11,921 (57)	122 (51)	1.0 (0.80, 1.3)	67 (57)	1.3 (0.87, 1.9)
Smoking pack-years
None	18,027 (75)	200 (73)	1.0 (referent)	93 (70)	1.0 (referent)
< 5 pack-years	2,639 (11)	22 (8)	0.85 (0.55, 1.3)	14 (11)	1.1 (0.64, 2.0)
5–18 pack-years	1,964 (8)	24 (9)	1.2 (0.77, 1.8)	12 (9)	1.3 (0.68, 2.3)
> 18 pack-years	1,388 (6)	29 (11)	1.5 (1.0, 2.2)*	13 (10)	1.5 (0.84, 2.7)
Grew up on farm
No	9,202 (39)	94 (35)	1.0 (referent)	47 (37)	1.0 (referent)
Yes	14,196 (61)	172 (65)	0.94 (0.73, 1.2)	80 (63)	0.93 (0.64, 1.3)
Years on farm
< 11 years	3,168 (14)	15 (6)	1.0 (referent)	10 (8)	1.0 (referent)
11–20 years	3,936 (17)	36 (13)	1.6 (0.88, 3.0)	18 (14)	1.3 (0.60, 2.9)
21–30 years	4,237 (18)	53 (20)	1.8 (0.99, 3.2)	24 (19)	1.3 (0.62, 2.9)
≥ 31 years	11,986 (51)	163 (61)	1.3 (0.75, 2.3)	74 (59)	1.1 (0.55, 2.3)
Note: ORs and 95% CIs for all RA cases and incident cases were adjusted for age. *p < 0.05.