Psychiatric Diagnosis and Classification - ResearchGate

INTERNATIONAL CLASSIFICATIONS 37
on the dimension. Clinicians are obliged to use categorical concepts, as they
must decide who is sufficientlyill to justifytreatment. But, in our efforts to
understand the relationships between social and biological variables, dimensional
models are far more appropriate [33]. Dimensional models are
more consistent with the polygenic or oligogenic) models of inheritance
favored for most mental disorders. These models assume that a number of
genes combine with one another and interact with the environmental factors
to cause the disorder. Persons can thus have various doses of the risk factors
that predispose to the illness and, depending on the dose, the severityof the
manifest condition mayvaryalong a continuum. Such approaches have
been shown to provide important clinical advantages with psychotic illnesses
[34] and personalitydisorders.
Though psychiatric disorders are construed to be disorders of brain chemistry,
a fundamental notion underpinning the classification systems is that
different disorders represent different classes of disturbance of mental life.
These categories thus must be understood as being distinct not onlyamong
themselves but also from ``normality''. In psychiatric classification, therefore,
categories can be seen as mathematical sets which, based on their properties,
can be reliablyand meaningfullyplaced in valid classes of similar objects.
These categories are often nominated bymeans of descriptive parameters
which then lead to categories that are big or small depending on our purpose,
as noted earlier. Psychiatric classifications attempt to define classes
not just bypositive defining parameters but also byexcluding other possibilities.
In other words, categories are defined according to the principle that
members of each categoryare more similar to each other than to members of
other categories. The attempt is thus to make the categories more internally
consistent. In addition, to separate or distance the categoryfrom others we
employexclusion criteria in order to prevent overlap between categories.
However, it is not sufficient just to have categories that are internally
consistent. Theymust also be meaningful, and membership of a category
must also be able to predict more about the member than what is said in the
inclusion rules alone. Further, once an exhaustive list of categories has been
achieved, theymust be sorted according to some larger principle in order to
make such a list more manageable and identifya purpose. This also ensures
the comparison of like with like, i.e. the comparison of categories that are
understood to be at the same level of complexity. This, however, means that
at the same level of hierarchywe cannot have categories that are determined
according to totallyunrelated parameters. In anycategorical system it is
imperative to ensure that the elements sort into discrete groups; otherwise,
the implication is that either the sorting rules were incorrect or the categories
did not exist.
Especiallywith regard to the categories of personalitydisorders, this
problem becomes exemplified when researchers assess everycriterion in