1 A discussion of the advantages and disadvantages of the categorical system of classifying abnormal behaviour, as exemplified by the Diagnostic and Statistical Manual of Mental Disorders Richard Lombard-Vance B.Sc. (Hons) Psychology student at National University of Ireland, Maynooth 2010 Introduction A number of categorical systems of abnormal behaviour classification exist, including the American Psychiatric Association’s (2000) Diagnostic and Statistical Manual of Mental Disorders (DSM IV-TR) and chapter five of the International Classification of Diseases (ICD10; World Health Organisation, 2007), among others. Both the DSM-IV-TR and the ICD-10 are widely used and the DSM in particular has sparked much controversy (e.g. Follette, 1994; Honos-Webb & Leitner, 2001). This controversy makes the DSM an ideal reference point for a discussion of the advantages and disadvantages of the categorical system of classifying abnormal behaviour. This discussion is especially relevant in the current climate with new versions of the ICD and DSM having entered their preparatory stages. This essay discusses these advantages and disadvantages, by covering the following areas: reliability, validity, comorbidity, labelling and alternative to the categorical systems. Note: I ǁouldŶ’t saLJ this is ŵLJ aƌea of edžpeƌtise…! This essaLJ is Ƌuite old now, and was written while I was a student. I submitted it as a writing sample many moons ago. Still, some people seem to have found it useful, so I’ll leaǀe it heƌe. - R