Handbook of Psychology, Volume 5, Personality and Social Psychology

68 Genetic Basis of Personality Structure

understanding the genetic basis of personality: the use of path-
ways models to evaluate competing models of personality.

Independent and Common Pathways Models

In heritability analyses, components of variance are esti-
mated by fitting models to the observed covariance matrices.
In the univariate case, the heritability of a variable is esti-
mated by comparing the similarity (estimated by Pearson’s r)
of MZ to DZ twins. In the bivariate case, common genetic
influences are suggested when the MZ cross-correlation
exceeds the DZ cross-correlation used to compute the genetic
correlation,rG.The multivariate extension of this idea is
found in two general classes of path analytic models that are
pertinent to personality research: independentandcommon
pathwaysmodels (see Figures 3.1 and 3.2; McArdle &
Goldsmith, 1990; Neale & Cardon, 1992). The independent
pathwaymodel specifies direct links from one or more ge-
netic and environmental influences common to each variable
and unique genetic and environmental effects to each vari-
able. The common pathwaysmodel is a more stringent ver-
sion of the independent pathways model. The primary
difference between the two models is that the common path-
waysmodel postulates that of the covariation in a set of vari-
ables is mediated by a single latent variable that has its own
genetic and environmental basis. Both models provide the
opportunity to examine variance specific to each variable—
that is, each lower-order trait. Factor analytic studies of

personality have been concerned with reducing the covari-

ance between lower-order traits to fewer factors. Residual

variance specific to each trait is neglected. Biometric path

models applied to twin data decompose this variance into

etiological components. This makes it possible to evaluate

the significance of these specific traits.

These models offer the opportunity to evaluate the hierar-

chical structure of personality by comparing the fit of the two

models to the same data set. The common pathways model

is the biometric equivalent to the traditional model of ex-

ploratory factor analysis used to delineate the phenotypic

structure of traits. As applied to each of the five-factor do-

mains, the model postulates a single latent factor for each do-

main that mediates the effects of genetic and environmental

effects on each lower-order trait. In the case of NEO-PI-R

Neuroticism, a latent variable of neuroticism is hypothesized

through which genetic and environmental factors influence

the six facets of Anxiety, Hostility, Depression, Self-

Consciousness, Impulsivity, and Vulnerability. In contrast,

the independent pathways model postulates direct genetic

and environmental effects on each facet trait. The fits of these

models provide an opportunity to evaluate different concep-

tions of personality structure. If the common pathways model

provides the best fit, the implication is that the hierarchical

structure of personality arises from the effects of higher-order

factors that have a genetic and environmental basis. The task

is then to explain how this entity differs from lower-order

or facet traits and the role it plays in the formation of the

Figure 3.1 Independent pathways model; G =additive genetic effects common to all variables, E =

nonshared environmental effects common to all variables, g =additive genetic effects unique to each vari-

able, and e =nonshared environmental effects unique to each variable

Independent Pathways Model

G
 additive genetic effects common to all variables

E 
 nonshared environmental effects common to all variables

g 
 additive genetic effects unique to each variable

e 
 nonshared environmental effects unique to each variables

Anxiety Hostility Depression Self-conscious Impulsiveness Vulnerability

G E

g e g e g e g e g e g e