Abstract

The concepts of reliability and validity are fundamental for evaluating psychiatric diagnosis, including the "operationalist" approach pioneered in DSM-III. This chapter explores the complexity of these psychometric concepts and their interrelations. Although reliability constrains validity it does not guarantee it, and pursuing reliability in diagnosis can reduce validity. It is widely believed that the operationalist emphasis on diagnostic reliability has compromised the validity of recent psychiatric classifications. In particular, writers have argued that the drive for atheoretical diagnostic criteria has come at the cost of phenomenological richness and psychodynamic complexity. This chapter argues that although the operationalist turn may have impaired the validity of psychiatric diagnosis in some respects, these criticisms must be balanced by an appreciation of its benefits. In addition, it is suggested that some criticisms rest on a misunderstanding of the goals of operational descriptions. They should be evaluated primarily on pragmatic grounds as identification procedures and judged on their success in serving epistemic and communicative functions. Operational descriptions should not be viewed as comprehensive definitions of clinical phenomena or judged on their failure to encompass the richness and complexity of mental disorders. A diagnostic system is best understood as an intentionally delimited instrument for enabling clinical inference and communication. In essence, it is a simplified pidgin with which clinicians who speak different first languages can conduct their shared business.