Clinical psychologists' theory-based representations of mental disorders predict their diagnostic reasoning and memory.

The theory-based model of categorization posits that concepts are represented as theories, not feature lists. Thus, it is interesting that the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994) established atheoretical guidelines for mental disorder diagnosis. Five experiments investigated how clinicians handled an atheoretical nosology. Clinicians' causal theories of disorders and their responses on diagnostic and memory tasks were measured. Participants were more likely to diagnose a hypothetical patient with a disorder if that patient had causally central rather than causally peripheral symptoms according to their theory of the disorder. Their memory for causally central symptoms was also biased. Clinicians are cognitively driven to use theories despite decades of practice with the atheoretical DSM.