CHAPTER 2
Classification
The underlying principles guiding
diagnostic groupings
Making it useful
Classification should facilitate communication among clinicians and
researchers rather than be a ‘train spotting’ exercise conducted for its
own sake. Classifying a child or adolescent’s disorder should be more
than a mere ‘naming of parts’; it should provide helpful pointers to:
aetiology; associated problems (thereby directing further enquiries and
investigations); choice of treatment; and prognosis. In general, it is possible
to use the same classification for all these purposes. Occasionally, however,
it is necessary to use different classifications for different purposes. For
example, clinicians will generally want to classify schizophrenia and
schizotypal personality disorder separately since they have very different
implications for treatment and prognosis. For a genetic researcher,
however, it may make more sense to combine the two into a category of
‘schizophrenia spectrum disorder’.
How do we decide whether a diagnostic scheme is following nature or
imposing arbitrary divisions, whether it is ‘carving nature at the joints’ or
hacking blindly through bones? To start with, a diagnostic category is un-
likely to be useful unless individuals with that diagnosis differ significantly
from individuals with other diagnoses. These differences must extend well
beyond the defining characteristics of the diagnostic group. In the case
of conduct disorder, for example, we need to know that individuals with
conduct disorder differ on average from individuals with other psychiatric
disorders not just in having more conduct problems (which is simply a
consequence of the definitions used) but in other respects as well, for
example, sex ratio, age of onset, socio-economic status, or association with
academic problems. Furthermore, at least some of the validating features
that distinguish different diagnoses should be clinically relevant. Thus, if
individuals with two diagnoses differ only in sex ratio and socio-economic
status, the two diagnoses should be merged rather than kept separate.
Demographic variables are certainly worth examining, but some of the
Child and Adolescent Psychiatry, Third Edition. Robert Goodman and Stephen Scott.
©c2012 Robert Goodman and Stephen Scott. Published 2012 by John Wiley & Sons, Ltd.
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