Twin-study research usually generates correlation tables similar to the
one found in Table 10.1. In this example, adult MZ and DZ twin pairs were
compared on the Big Five personality traits (Chapter 7). As seen in the table,the MZ twin pairs were more similar than the DZ twin pairs in each case
(Riemann, Angleitner, & Strelau, 1997). The data in the table are similar to
those obtained in other twin studies looking at different measures of the BigFive dimensions (Borkenau, Riemann, Angleitner, & Spinath, 2001; Jang,
Livesley, & Vernon, 1996; Jang, McCrae, Angleitner, Riemann, & Livesley,
1998; Loehlin, McCrae, & Costa, 1998; McCrae, Jang, Livesley, Riemann, &Angleitner, 2001). When we combine twin studies examining many different
personality traits, we find that MZ twins ’scores tend to correlate on average
about .50, whereas DZ twin correlations are in the .25 to .30 range (Loehlin,
1992). Behavior genetics researchers plug these numbers into formulas to esti-
mate that between 40% and 50% of the stability in our adult personalities
can be attributed to what we inherit from our parents (Krueger & Johnson,
2008; Loehlin, 1992; Plomin, Chipuer, & Loehlin, 1990).
Other methods for teasing apart genetic and environmental influences
also find evidence for genetic influence, but usually not as strong as in thetwin-study data (Plomin & Caspi, 1999). One example comes from research
with adopted children. When children are raised from birth by someone othersame same
same differentMonozygotic (MZ)
Twins
Environment
GeneticsDizygotic (DZ)
Twins
FIGURE 10.1 Twin-Study Research Diagram
TABLE10.1
Correlations from a Twin Study
MZ Twins DZ Twins
Neuroticism .53 .21
Extraversion .56 .33
Openness .54 .35Agreeableness .42 .24Conscientiousness .54 .23
Source: Riemann, Angleitner, and Strelau (1997).Heritability of Personality Traits 255