Diagnosis, diagnostic formulations, and classification

The differences among diagnosis, diagnostic formulations and classification, and between clinical and research classifications, are discussed. The current impossibility of basing classification on brain circuitry is noted. It is argued that both dimensional and categorical approaches are useful, and should be combined because they provide different information. The validation of diagnostic categories is reviewed in relation to age trends and sex differences; familiality and genetics; psychosocial correlates; long-term course; drug response; cognitive impairments; and biological findings. A 3-level organisational structure is supported.