Table 3.

Hazard Ratios and Incidence Rates for Dementia by Birth Cohort

Pre-1935 birth cohort Year of birth 1921–1934 (N = 4,039); ages 52–66 on study enrollment 1986–1988
No. of births	Dementia incidence rate per 1,000 person-years	Unadjusted HR (95% CI)	Model 1 HR (95% CI)	Model 2 HR (95% CI)	Model 3 HR (95% CI)	Model 4 HR (95% CI)
0–1	11.49	0.97 (0.79–1.19)	0.87 (0.71–1.07)	0.86 (0.70–1.6)	0.81 (0.65–1.00)	0.77 (0.62–0.96)
2 (Ref)	12.25	1	1	1	1	1
3–4a	10.72	0.85 (0.72–1.00)	0.84 (0.71–0.98)	0.83 (0.71–0.98)	0.81 (0.69–0.96)	0.79 (0.67–0.93)
5+b	11.20	0.91 (0.76–1.09)	0.95 (0.80–1.12)	0.74 (0.62–0.90)	0.72 (0.59–0.87)	0.70 (0.57–0.85)

1935 or later birth cohort Year of birth 1935–1945 (N = 3,882); ages 45–54 on study enrollment 1986–1988
No. of births	Dementia incidence rate per 1,000 person-years	Unadjusted HR(95% CI)	Model 1 HR(95% CI)	Model 2 HR(95% CI)	Model 3 HR(95% CI)	Model 4 HR(95% CI)
0–1	3.29	1.14 (0.80–1.64)	1.06 (0.73–1.52)	1.06 (0.74–1.52)	1.05 (0.72–1.52)	1.03 (0.71–1.51)
2 (Ref)	3.15	1	1	1	1	1
3–4a	3.70	1.21 (0.93–1.57)	1.08 (0.83–1.41)	1.03 (0.79–1.35)	1.04 (0.79–1.37)	1.02 (0.77–1.35)
5+b	6.31	2.32 (1.74–3.09)	1.39 (1.03–1.88)	1.11 (0.82–1.52)	1.18 (0.86–1.63)	1.14 (0.82–1.58)

Bold values indicate confidence interval does not cross 1.

Birth cohorts were divided into 1921–1934 and 1935–1945, based on median year of birth of 1935.

Model 1: age; stratified by race-center.

Model 2: age, education; stratified by race-center.

Model 3: age, education, smoking, cholesterol, alcohol use, leisure index, APOE; stratified by race-center, hypertension, diabetes, BMI category.

Model 4: age, education, smoking, cholesterol, alcohol use, leisure index, APOE; stratified by hypertension, diabetes, BMI category, race-center, stroke.

Models 3 and 4 included age modeled as age × time interaction, due to violated proportional hazards assumptions.

^a p-value for interaction = 0.05.

^b p-value for interaction <0.001.