Table 3.

Effects of Secondhand Smoke Exposure and Vascular Disease on Dementia Incidence, per Cox Proportional Hazards Marginal Structural Models,^a in the Cardiovascular Health Cognition Study From 1991 to 1999

Variable	Model 1		Model 2		Model 3		Model 4
	HR	95% CI	HR	95% CI	HR	95% CI	HR	95% CI
Clinical vascular diseaseb	1.65	0.62, 3.16	1.56	0.53, 3.10	1.59	0.62, 3.21	1.60	0.60, 3.27
SHS exposurec
16–25 years	1.02	0.48, 1.88	1.08	0.53, 2.02	1.02	0.48, 1.90	1.13	0.38, 2.43
>25 years	1.43	0.80, 2.32	1.28	0.71, 2.14	1.46	0.82, 2.40	0.81	0.34, 1.50
Subclinical MRI measuresd
Infarct ≥3 mm			0.90	0.50, 1.62
Infarct <3 mm			1.67	0.92, 2.98
White matter disease			2.65	1.70, 4.34
Subclinical carotid artery measuresd
Internal artery thickness >80th percentile			1.60	0.80, 3.07	1.52	0.77, 2.92
Common artery thickness >80th percentile			1.07	0.66, 1.69	1.08	0.66, 1.73
Stenosis >25%					0.99	0.59, 1.67	0.76	0.40, 1.41
Stenosis >25% × SHS exposure 16–25 years							0.87	0.21, 3.35
Stenosis >25% × SHS exposure >25 years							3.00	1.03, 9.72

Abbreviations: CI, confidence interval; HR, hazard ratio; MRI, magnetic resonance imaging; SHS, secondhand smoke.

^aAll models adjusted for age, gender, and education. Other variables listed in the Materials and Methods section of the text were included in the “treatment” model; therefore, it was not necessary to adjust for them in the marginal structural models. Refer to the Appendix for more details. Results were similar when subclinical MRI measures and subclinical carotid artery measures were included in the same model to determine whether their effects were independent, and when Modified Mini-Mental State Examination score was included as a stratification variable to further control for residual confounding by baseline cognitive function, education, and socioeconomic status.

^bMarginal (population) relative hazard of clinical cardiovascular disease on dementia at time t for a given stratum of age, SHS exposure, gender, and education.

^cAssociated relative hazard of dementia at time t for various SHS exposure levels compared with that for subjects with 0–15 years of SHS exposure for a given stratum of age, gender, and education, independent of any effects of cardiovascular disease.

^dAssociated relative hazard of dementia at time t for subjects for various subclinical MRI measures (model 2), subclinical carotid artery measures (model 3), or interactions between SHS and subclinical carotid artery measures (model 4) for a given stratum of age, gender, education, and SHS exposure, independent of any effects of cardiovascular disease.