Classification in Psychiatry: Nosological Systems

1. Overview & Epidemiology

Nosology = the science of classifying diseases. In psychiatry it groups disorders into named, defined categories so that clinicians, researchers, and statisticians use the same language for the same condition.

Why classify? — the aims of modern psychiatric classification

This is the conceptual core of the topic and is tested verbatim in PSY - 2.42. A modern classification system exists to:

1. Define mental disorders through explicit, operationalized criteria — replacing vague descriptive prose with checklists (symptom counts, durations, exclusions).
2. Enable scientific investigation — a shared, reproducible definition lets differe