Limitations of the Categorical Approach

'DSM-IV is a categorical classification that divides mental disorders into types based on criteria sets with defining features. This naming of categories is the traditional method of organising and transmitting information in everyday life and has been the fundamental approach used in all systems of medical diagnosis. A categorical approach to classification works best when all members of a diagnostic class are homogeneous, when there are clear boundaries between classes, and when the different classes are mutually exclusive. Nonetheless, the limitations of the categorical classification system must be recognised.

In DSM-IV, there is no assumption that each category of mental disorder is a completely discrete entity with absolute boundaries dividing it from other mental disorders or from no mental disorder. There is also no assumption that all individuals described as having the same mental disorder are alike in all important ways. The clinician using DSM-IV should therefore consider that individuals sharing a diagnosis are likely to be heterogeneous even in regard to the defining features of the diagnosis and that boundary cases will be difficult to diagnose in any but a probabilistic fashion. This outlook allows greater flexibility in the use of the system, encourages more specific attention to boundary cases, and emphasises the need to capture additional clinical information that goes beyond diagnosis. In recognition of the heterogeneity of clinical presentations, DSM-IV often included polythetic criteria sets, in which the individual need only present with a subset of items from a longer list (e.g., the diagnosis of Borderline Personality Disorder requres only five out of nine items).

It was suggested that the DSM-IV classification be organised following a dimensional model rather than the categorical model used in the DSM-III-R. A dimensional system classifies clinical presentations based on quantification of attributes rather than the assignment to categories and works best in describing phenomena that are distributed continuously and that do not have clear boundaries. Although dimensional systems increase reliability and communicate more clinical information (because they report clinical attributes that might be subthreshold in a categorical system), they also have serious limitations and thus far have been less useful than categorical systems in clinical practice and in stimulating research. Numerical dimensional descriptions are much less familiar and vivid than are the categorical names for mental disorders. Moreover, there is as yet no agreement on the choice of the optimal dimensions to be used for classification purposes. Nenetheless, it is possible that the increasing research on, and familiarity with, dimensional systems may eventually result in their greater acceptance both as a method of conveying clinical information and as a research tool'.

DSM IV-TR pp, xxxi-xxxii

very interesting, thank you, alex.