IPDE - Extranet Systems - World Health Organization

84 A. W. Loranger
Categories and dimensions
The prevailing systems of disease classification are categoric. They define
the features of disorders, and ideally the categories have points of rarity
with normality and other disorders. Although such nosologies sometimes
fall short of the ideal, their value as shorthand forms of communication
accounts for their widespread acceptance. However, proponents of what
has come to be known as the 'dimensional' approach question the applicability
of the categorical method to personality disorders.14 One argument
is that if PDs are not truly dichotomous in nature, reliability should
improve with the use of dimensions because their measurement would
incorporate more information than that provided by categories alone.
Critics sometimes overlook the fact that categories and dimensions
need not be mutually exclusive, witness their harmonious coexistence in
the classification of mental retardation and hypertension. Following that
tradition, the IPDE was designed to provide categorical diagnoses and
dimensional scores based on the categories. The results of the present
study demonstrate the favorable effect of these scores on the reliability
of the IPDE. This is illustrated, e.g., by paranoid personality, the disorder
with the least stability. Although the DSM-111-R kappa was only
.24, the stability of the paranoid dimensional score was 0.68 (0.74 with
correction for attenuation). The stability of all of the DSM-III-R dimensional
scores ranged from 0.68 to 0.92 (0.74 to 0.95 corrected), with a
median of 0.77 (0.83 corrected). The corresponding correlations for the
ICD-10 dimensions ranged from 0.65 to 0.86 (0.71 to 0.90 corrected).
with amedian of 0.77 (0.82 corrected).
These findings provide a striking example of the advantage of supplementing
a categorical conclusion about the presence or absence of a specific
PD with dimensional information about the traits that underlie the
decision-making process. The IPDE dimensional scores include information
about accentuated normal traits below the threshold required for
a PD. A measure based on pathological traits alone consists of the number
of criteria that a patient meets on a particular disorder. Table 8 (see
chapter 'Results') reveals that this coarser measure is almost invariably
associated with lower reliabilities than the dimensional scores, although
thedifferences are not usually great.
Clinical acceptability and validity of the IPDE
At the conclusion of the study, a questionnaire concerning the IPDE was
completed by all of the inte~ewers and discussed at length at the meeting