Rep36 Understanding Personality Disorder

1.1.7 Statistical deviation and personality
dysfunction
Although extreme manifestation of certain traits
or dimensions seems necessary to define
abnormalities of personality, it may not be
sufficient to identify disorder or dysfunction, as
indicated by failures to perform social and
occupational roles. Psychologists generally see
normality and abnormality as falling on a
quantitative continuum. A trait is abnormal
when its manifestation is extreme relative to the
population average, extremeness commonly
being defined arbitrarily in psychological tests by
the statistical criterion of two standard deviations
from the mean, a position occupied by less than
2 per cent of the population. In these terms,
disorders of personality are extreme variants of
normal personality, and can hence be described
by reference to dimensions of personality, such
as the five-factor model. 
However, personality dysfunction is not
necessarily expressed in extreme traits because it
depends on the context. Some people may have
extreme traits but function adequately because
their characteristics are not an impediment for a
particular role or setting. This is recognised in
the notions of discordant personality (Foulds,
1971) or personality accentuation (Tyrer, 2000),
which fall short of disorder. The DSM-IV
definition of personality disorders as traits that
are inflexible and maladaptive and cause
significant functional impairment or subjective
distress follows Schneider’s original distinction
between abnormal personalities and those who
‘suffer’ from their abnormality (Livesley, 2001).
This also implies that statistical deviation is
necessary but not sufficient to define dysfunction. 
The dysfunctional component of personality
disorder may to some extent be independent of
extremes of personality. There is a clear parallel
with learning disability. This is not identified by
low intelligence alone but by dysfunctional
adaptation under conditions requiring
intellectual ability. One view is that dysfunction
needs to be defined in terms of the basic
functions of personality (Livesley, 2001). From
an evolutionary perspective these are to attain
the universal life tasks of: 
I
A stable self-system (identity, representations
of self and others);
I
Satisfying interpersonal functioning
(attachment, intimacy, affiliation); 
I
Societal/group relationships (prosocial, co-
operative behaviour);
Dysfunction or disorder is proposed to arise
from impairment in the organisation, integration
or regulation of underlying personality processes
involved in these tasks. The personality and
disorder components may therefore need to be