Psychiatric Diagnosis and Classification - ResearchGate

18 PSYCHIATRIC DIAGNOSIS AND CLASSIFICATION
into account when developing, adapting, or translating diagnostic classifications.
Needs of Researchers
Both DSM-III and its successors and, to a lesser extent, ICD-10 were welcomed
and quickly adopted by researchers as rigorous diagnostic standards.
However, the performance of a classification as a research tool needs
to be evaluated against a number of different requirements that are not
always compatibleÐfor example, the type of diagnostic criteria needed for
clinical trials or for biological research may not be suitable for epidemiological
surveys.
The use of restrictive DSM-IV or ICD-10 definitions, rather than broader
clinical concepts, as sampling criteria in recruiting subjects for clinical or
epidemiological research carries the risk of replacing random error due to
diagnostic inconsistencies) with systematic error due to a consistent exclusion
of segments of the syndrome). For example, the DSM-IV requirement of
at least six months' duration of symptoms plus the presence of social or
occupational dysfunction for a diagnosis of schizophrenia is likely to bias
the selection of populations for biological, therapeutic, or epidemiological
longitudinal studies. It would certainly make little sense to study the variation
in course and outcome in a clinical population that had already been
pre-selected for chronicity by applying the six-month duration criterion.
Major studies of the molecular genetics of psychoses, usually involving
collaborative consortia of investigators and a considerable investment of
resources, are predicated on the validity of DSM-III-R or DSM-IV criteria.
However, so far no susceptibility genes have been identified and few of the
reports of weak positive linkages have been replicated [44]. In addition to
the likely genetic heterogeneity of psychiatric disorders across and within
populations, it appears possible that ``current nosology, now embodied in
DSM-IV, although useful for other purposes, does not define phenotypes for
genetic study'' [45]. In the absence of genes of major effect, the chances of
detecting multiple genes of small or moderate effect depend critically on
the availability of phenotypes defining a characteristic brain dysfunction
or morphology. The ``disorders'' of current classifications, defined by polythetic
criteria, are probably surface phenomena, resulting from multiple
pathogenetic and pathoplastic interactions. They may also be masking substantial
phenotypic variation in symptomatology and outcome. Such variation
would hinder genetic analysis and might nullify the power of the
sample to generate high-resolution data. In addition to a better syndromal
definition at the clinical symptom and course level, future developments
of diagnostic systems for research are likely to involve supplementing the