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. Author manuscript; available in PMC: 2011 Aug 19.
Published in final edited form as: J Health Soc Behav. 2010 Mar;51(1):108–123. doi: 10.1177/0022146509361195

Figure 2.

Figure 2

Yearly Heritability Estimates for Regular Smoking in the United States: 1922–1968.

Note: Data come from the 1995 National Survey of Midlife Development in the United States (MIDUS) [Brim et al. 1996]. Estimates are obtained from a series of multivariate Cox regression models with shared frailty among twin pairs, and they describe the heritability of regular smoking for each year of birth. The bars around each point estimate describe the 95% confidence intervals for each year. These confidence intervals were bootstrapped from 200 runs for each zygosity using the coxph package for R 2.7.1 for all years between 1922 and 1968. Each birth year contains the four years before and after and thus describes a nine-year window for the estimated genetic influences on smoking at that time.