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. Author manuscript; available in PMC: 2010 Sep 1.
Published in final edited form as: Psychol Sci. 2009 Aug 14;20(9):1146–1152. doi: 10.1111/j.1467-9280.2009.02425.x

TABLE 1. Maximum Likelihood Estimates of Correlations Between Twins' Armed Forces Qualification Test Scores at Age 20 and at Age 55.

Twin Twin 1 at age 20 Twin 2 at age 20 Twin 1 at age 55
Monozygotic twins
 Twin 2 at age 20 .75 — —
 Twin 1 at age 55 .74 .70 —
 Twin 2 at age 55 .69 .75 .75
Dizygotic twins
 Twin 2 at age 20 .52 — —
 Twin 1 at age 55 .70 .42 —
 Twin 2 at age 55 .45 .79 .47

Note. Age 20 Armed Forces Qualification Test (AFQT) scores served as baseline. The Age 55 AFQT scores were taken during the Vietnam Era Twin Study of Aging. All correlations were statistically significant (p < .001).