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. Author manuscript; available in PMC: 2010 Sep 1.
Published in final edited form as: Intelligence. 2009 Sep 1;37(5):466–478. doi: 10.1016/j.intell.2009.05.006

Figure 2.

Figure 2

Model of moderation of genetic and environmental influences on Grade Point Average or Educational Attainment (GPA/Ed) in the presence of possible overlap in genetic and environmental influences on the two variables, shown here for one member of a twin pair only. A refers to genetic influences, C to shared environmental influences, and E to nonshared environmental influences. Variance in GPA/Ed can result from any combination of the labeled paths: A, C, and/or E common to IQ and GPA/Ed and/or A, C. and/or E unique to GPA/Ed. Each of these paths can vary with level of IQ, shown by M for moderator in the above path equations. The model includes the paths representing the influences on IQ as well, though they are not labeled in the figure.