Rep36 Understanding Personality Disorder

particularly for treatment planning or measuring
clinical outcomes because of the problems with
reliability and validity outlined above. 
Personality and Personality Disorder
1.1.5 Categories and dimensions of
personality disorder
A major problem with the current classifications
is that they rely on a categorical, all-or-none
system for distinguishing types of disorder and
for diagnosing individual problems. Categorical
classification of personality disorder follows a
medical model that implies qualitative
distinctions between normality and abnormality
(i.e. present or absent) and clear boundaries
between categories. The alternative is a
dimensional approach that assumes only
quantitative distinctions (i.e. varying degrees of
dysfunction). 
Dimensional and categorical descriptions of
personality disorder are not incompatible
(Widiger & Frances, 1994). Categorical
diagnoses can be thought of as based on a
continuous dimension where a relatively
arbitrary diagnostic cut-off has been applied.
Evidence from research indicates that
dimensional conceptions of personality disorder
more accurately represent the organisational
structure of personality dysfunction (Livesley,
2001). There are therefore good grounds for
translating the categorical classification of
personality disorder into dimensions of human
variation identified through theory and research
on the structure of normal personality.

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1.1.6 The structure of personality
In personality research, traits are viewed as part
of a hierarchy. Particular personality traits (such
as dominance) are inferred from a person’s
tendency to behave in particular ways (such as
taking the lead in group activities). Personality
types or categories are identified when certain
traits occur together in many individuals.
Categories of personality disorder are constructs
based on such personality types.
Psychologists have used statistical methods
such as factor analysis to investigate how traits go
together to form dimensions. Research has
established that relationships between the vast
number of normal range traits denoting
behavioural, emotional and cognitive
dispositions reflect a few robust dimensions. 
While the number of dimensions identified
has ranged from three to seven (Watson, Clark &
Harkness, 1994), over time it has become
apparent that most variation in personality is
accounted for by the ‘Big Five’ factors. The ‘Big
Five’ dimensions are Neuroticism vs stability,
Extraversion vs introversion, Agreeableness vs
antagonism, Conscientiousness vs lack of self-
discipline, and Openness to experience vs
rigidity. These five factors are believed to
represent biologically derived basic tendencies,
which are instrumental in shaping attitudes,
goals, relationships and the self-concept, and
influence our interactions with the social and
physical environment (McCrae & Costa, 1996).
The five-factor model is widely regarded as
the dimensional model most relevant to
understanding personality disorder. It enables
personality and personality disorder to be
understood in terms of a small number of
dimensions, and it allows personality disorder to
be understood in the wider context of
personality research. Further, studies of traits
defining personality disorder also reveal that
their structure follows that of the five-factor
model (Clark, Livesley, Schroeder & Irish, 1996).
We do not therefore need a separate trait
language for describing disorders of personality.
Although dimensions do not provide a
diagnostic classification in the traditional sense,
it is nevertheless possible to represent the
current classes of personality disorder
dimensionally as combinations of extremes on
different dimensions (Widiger & Frances, 1994).