Table 2.

Pairwise Concordance in the Timing of Smoking Desistance by Zygosity

	Proportion of co-twins who quit prior to censoring	Mean years difference in quitting including censored durations	N
Identical twins (MZ)	.647	10.08 (6.79)	363
Fraternal twins (DZ)	.554	11.02 (6.57)	233
pr.(MZ=DZ)	<.022	<.049

Note: See Truett et al. (1994) and Eaves et al. (1999) for additional information about this study. Standards deviations are reported in parentheses.

Source: Data on twin pairs come from a large population-based birth registry for the Commonwealth of Virginia and the American Association of Retired Persons. This study only uses data in which both members of the twin pair report regular smoking at some point during the study.