cepts of interpersonal interaction were also central to formulations of
personality disorders (Millon, 1981; Widiger & Frances, 1985) andwere ultimately incorporated in the 1994 edition of the American Psy -
chiatric Association’s official diagnostic system, the DSM-IV . These per -
sonality disorders can be interpreted as maladaptive variants of normal
personality traits.
The Quest for a Unified System
Historically , competition among these systems has been a preoccupa -
tion of personality psychologists, and the lack of a single, unified model
has significantly hindered progress in the field. Researchers from differ -
ent schools could not easily communicate, so results could not be com -
pared. A study of age changes on the GZTS would not speak to the con -
cerns of adherents to Murray’s system of needs (discussed above), so a
separate study of age changes in needs might be required. Research ef-forts were at best inefficient.
If all the different systems really identified distinct parts of person-
ality , as they appeared to do in principle, the search for a comprehensiveyet parsimonious model would be futile. But numerous studies haveshown that there are important overlaps among the various systems. Al-though needs may seem to be quite different from personality disordersand from Jungian functions, the measures of these concepts turn out tohave much in common. Neuroticism and Extraversion play a large rolein many personality inventories—so much so that Wiggins (1968)called these the “Big T wo.” Unfortunately , the correspondences are oftenobscured by the labels psychologists have chosen for their scales. T womeasures with the same label may measure different traits, and twomeasures of the same trait may have very different labels.
The identification of new traits might seem to be the equivalent of
the entomologist’s classification of insects or the astronomer’s catalog -
ing of stars. In fact, it is something quite different. It is easy enough to
identify a beetle from its picture and description or to characterize a starby its exact position in the sky . But we cannot pin up specimens of anxi -
ety or personal insecurity or Neuroticism or guilt-proneness and com -
pare them, nor do we have a map of the “personality sphere” that we
can use to check the location of a trait. How do we know whether thetraits in one system are the same as those in another system under dif -
ferent names?32 PERSONALITY IN ADULTHOOD