428 Part V Biological/Evolutionary Theories
system and physiology would be the foundation for the personality trait of neu-
roticism. To be sure, there is more research to be done and not all of the past
research confirms each aspect of Eysenck’s theory. But overall, a biological basis
of neuroticism seems to be established.Critique of Eysenck’s Biologically Based Theory
First, does Eysenck’s biologically based theory generate research? On this crite-
rion, it must be rated very high. Figure 14.5 shows the comprehensiveness of
Eysenck’s personality theory. The middle square embraces the psychometric prop-
erties of his theory; that is, psychoticism, extraversion, and neuroticism. This fig-
ure also shows that Eysenck’s personality theory is much more than a simple
classification. The genetic and biological antecedents of behavior are suggested by
the two squares on the left, whereas some of the consequences, or outcomes, of
Eysenck’s research are found in the two squares on the right. These consequences
are a result of experimental studies on conditioning, sensitivity, vigilance, percep-
tion, memory, and reminiscence. Areas of research on social behavior are shown
in the box on the far right and include such topics as sociability, criminality,
creativity, psychopathology, and sexual behavior. Eysenck and his colleagues have
reported significant amounts of research in these and other fields of research.
Second, are trait and factor theories falsifiable? On this criterion, trait and fac-
tor theories receive a moderate to high rating. Some of Eysenck’s research results—
for example, his investigations of personality and disease—have not been replicated
by outside researchers. His biological theory, because it makes specific predictions, is
falsifiable. Results, however, are mixed, with some of his predictions being confirmed
(e.g., optimal arousal) and some not (e.g., cognitive processing speed).
Third, trait and factor theories are rated high on their ability to organize
knowledge. Because Eysenck’s model of personality is one of the few to take biol-
ogy seriously, it is one of the only theories that can explain the observations that
individuals differ in behavior at birth and that genetics accounts for roughly half
of the variability in individual differences.
Fourth, a useful theory has the power to guide the actions of practitioners,
and on this criterion, biological theories rank relatively low. Although these theo-
ries do a good job of explaining the origins of personality differences, they do not
easily lend themselves to practical guides for teachers, parents, and even counsel-
ors. On this criterion, biological theory rates relatively low.
Are trait and factor theories internally consistent? Again, the rating must be
equivocal. The theory of Eysenck is a model of consistency, but when compared to
the Five-Factor model, Eysenck’s model is somewhat inconsistent. Eysenck remained
convinced that his Giant Three factors were superior to the Big Five model. This
inconsistency presents a problem, especially because factor analysis is a precise
mathematical procedure and because factor theories are heavily empirical.
The final criterion of a useful theory is parsimony. Like McCrae and Costa’s
Five-Factor Model, Eysenck’s model of personality is also based on factor analy-
sis and therefore provides a very parsimonious explanation of personality. Indeed,
with only three major dimensions, Eysenck’s model is even more parsimonious
than the Five-Factor approach.