733 Assessment
 Measures
A growing body  of scientific evidence favors dimensional concepts in the diagnosis
of mental disorders. The limitations of a cate gorical approach to diagnosis include the fail-
ure to find zones of rarity between diagnoses (i.e., delineation of mental disorders from one
another by natural boundaries), the need for in termediate categories like schizoaffective dis-
order, high rates of comorbidity, frequent not-otherwise-specified (NOS) diagnoses, relative
lack of utility in furthering the identification  of unique antecedent validators for most men-
tal disorders, and lack of treatment specif icity for the various di agnostic categories.
From both clinical and research perspectiv es, there is a need for a more dimensional
approach that can be combined with DSM’s se t of categorical diagnoses. Such an approach
incorporates variations of features within an in dividual (e.g., differential severity of indi-
vidual symptoms both within and outside of a disorder’s diagnostic  criteria as measured
by intensity, duration, or number of symptoms , along with other features such as type and
severity of disabilities) rather than relying on a simple yes-or-no approach. For diagnoses
for which all symptoms are needed  for a diagnosis (a monothetic  criteria set), different se-
verity levels of the constituent symptoms may be noted. If a threshold endorsement of
multiple symptoms is needed, su ch as at least five of nine symptoms for major depressive
disorder (a polythetic criteria  set), both severity levels and different combinations of the
criteria may identify more ho mogeneous diagnostic groups.
A dimensional approach depending primarily on an individual’s subjective reports of
symptom experiences along with the clinician’s interpretation is consistent with current
diagnostic practice. It is expected that as  our understanding of basic disease mechanisms