TABLE 2.

Characteristics of Participants and Unadjusted Incidence Rate Ratios for Rheumatoid Arthritis and Autoimmune Disease in Female Medicare Beneficiaries, Health and Retirement Study, 1991–2007

		Rheumatoid arthritis		Autoimmune diseasea
	n, sample	IRR	95%CI	IRR	95%CI
Age at first interview:
<65 years	977	1.00	(reference)	1.00	(reference)
65–69 years	720	0.48	0.31, 0.73	0.53	0.37, 0.76
70–74 years	1664	0.49	0.34, 0.70	0.45	0.34, 0.61
≥75 years	1360	0.64	0.46, 0.87	0.53	0.39, 0.71
Race:
Caucasian	3989	1.00	(reference)	1.00	(reference)
African-American	617	1.33	0.91, 1.94	1.14	0.85, 1.52
Other	115	1.60	0.77, 3.34	1.25	0.64, 2.43
Hispanic:
Not Hispanic	4439	1.00	(reference)	1.00	(reference)
Mexican-American	151	1.27	0.88, 1.85	1.11	0.73, 1.70
Other Hispanic	131	1.30	0.54, 3.11	1.13	0.53, 2.40
Religion:
Jewish	139	1.89	1.14, 3.13	1.87	1.27, 2.76
Non-Jewish	4582	1.00	(reference)	1.00	(reference)
Body mass index at first interview:
Underweight (<18.5 kg/m2)	127	1.00	(reference)	1.00	(reference)
Normal (18.5–24.9 kg/m2)	1937	1.30	0.51, 3.29	1.73	0.72, 4.19
Overweight (25.0–29.9 kg/m2)	1726	1.47	0.58, 3.71	1.81	0.77, 4.28
Obese (≥30.0 kg/m2)	931	1.83	0.72, 4.66	2.27	0.92, 5.55
Smoked at first interview:
No	4148	1.00	(reference)	1.00	(reference)
Yes	573	0.99	0.67, 1.46	1.08	0.79, 1.48
Number of children:
0	1480	1.00	(reference)	1.00	(reference)
1	2169	1.30	0.79, 2.14	1.35	0.94, 1.95
2	4198	0.84	0.53, 1.32	0.91	0.66, 1.28
≥3	8934	1.09	0.68, 1.75	1.02	0.72, 1.45
Transfusion-related visit:
No	4182	1.00	(reference)	1.00	(reference)
Yes	539	1.69	1.25, 2.30	1.60	1.23, 2.07
Infection-related visit:
No	3222	1.00	(reference)	1.00	(reference)
Yes	1499	1.42	1.13, 1.80	1.31	1.04, 1.66
End-stage renal disease:
No	4667	1.00	(reference)	1.00	(reference)
Yes	54	3.68	1.88, 7.19	2.86	1.53, 5.32
Heart disease:
No	2945	1.00	(reference)	1.00	(reference)
Yes	1776	1.52	1.16, 2.01	1.41	1.13, 1.76
Stroke:
No	3872	1.00	(reference)	1.00	(reference)
Yes	849	1.01	0.75, 1.37	1.02	0.79, 1.30
Diabetes mellitus:
No	3784	1.00	(reference)	1.00	(reference)
Yes	937	1.07	0.80, 1.43	1.13	0.87, 1.46
Cancer:
No	3829	1.00	(reference)	1.00	(reference)
Yes	892	1.10	0.86, 1.42	1.23	0.97, 1.56
Region of residence:
Northeast	838	1.09	0.63, 1.87	1.41	0.88, 2.25
Midwest	1228	0.86	0.55, 1.34	0.99	0.71, 1.39
South	1860	1.41	0.91, 2.17	1.42	1.00, 2.04
West	795	1.00	(reference)	1.00	(reference)

Abbreviations: IRR, incidence rate ratio; CI, confidence interval.

^aIncludes rheumatoid arthiritis, Graves' disease, systemic lupus erythematosus, Hashimoto's disease, Sjoren syndrome, celiac disease, systemic sclerosis, multiple sclerosis.