CHAPTER 3
Epidemiology
Epidemiology can be defined as the study of the distribution of disorders
and associated factors in defined populations. The defined population may
be a representative community sample, but it might also be a high-risk or
particularly informative sample, for example, all children with hemiplegic
cerebral palsy in London, or all children living in an area with high lead
pollution.
Advantages of an epidemiological approach
1 Essential to estimate incidence and prevalence – relevant for planning
service provision for the whole population.
2 Being free (or freer) of referral bias, epidemiological studies are better
than clinic-based studies as sources of accurate information about de-
mographic characteristics, associated problems, and natural history. All
these benefits are important for studies aiming to improve classification.
They are also relevant to aetiology, with causal relationships being
suggested, but not proven, by epidemiological associations that are
strong, dose-related, and persistent despite controlling for ‘confounders’
such as socio-economic status. The power of epidemiological studies
to distinguish between causal and non-causal associations is increased
when the study is longitudinal or capitalises on a ‘natural experiment’
such as adoption, twin birth or migration.
3 Useful for examining protective factors. For example, why do some
children remain well adjusted despite exposure to acrimonious marital
conflict? Clinic-based studies are almost bound to miss the children who
have benefited most from exposure to protective factors.
Epidemiological studies are not always
the best approach
1 A detailed study of a few (unrepresentative) cases may be more instruc-
tive than a superficial study of a large and representative population.
Understanding phenylketonuria or general paresis of the insane did not
require an epidemiological approach.
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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