For many of the conditions with which psychiatry is concerned, there is still no anatomical or physiological abnormality that is reliably found in those affected with the conditions and not in other people. Some evidence exists that, for instance, severe and chronical psychopathological symptoms such as persistent auditory hallucinations, may be linked to structural brain abnormalities in certain subgroups of schizophrenic patients. However, such associations are not well-established as yet and the research in this field does not have practical implications for psychiatric assessment so far.

Because objective (physical) indices for measuring (the severity of) psychopathological states have hardly been available up to now, the rating scale is an essential instrument in clinical (psychopharmacological) research.