One prediction that arises from the
in this study
diagnostic substitution hypothesis is
was small
that the increase in autism prevalence
this research
in recent years will have been
adds weight
accompanied by a corresponding
to the
decrease in the prevalence of other
diagnostic
disabilities. There is some evidence
substitution
that this is the case. For example, one
hypothesis.
Diagnostic substitution: When one diagnosis is replaced by a different diagnosis because of improved understanding and/or changing diagnostic criteria.
study performed in the United States investigated the prevalence of disabilities
If changing diagnostic criteria are
among children in special needs
largely responsible for the increase in
education from 1984-2003. It was found
identified cases of autism then when
that increases in autism prevalence were
the same criteria are applied over time
significantly associated with decreases
the prevalence of autism should remain
in the number of recorded cases of
the same. Chakrabarti & Fombonne
intellectual disabilities over this time5.
(2005) repeated a study they had previously performed several years before
Other studies have attempted to
of autism prevalence among children
determine whether the broadening
in Stafford. They rigorously applied the
of diagnostic criteria is responsible for
same methods for autism diagnosis
the increase in autism prevalence by
they had previously used to a group
applying modern criteria for autism
of children born during a later period.
to people who had previously been
The prevalence figure for the later study
diagnosed with other behavioural
remained the same which argued
and intellectual disabilities. Bishop
against a genuine increase in the
et al. (2008) applied contemporary
incidence of autism6.
diagnostic criteria for autism to a group of adults who had been diagnosed
Another way of attempting to determine
with language disorders as children .
if there is a real increase in the
Developmental language disorders are
occurrence of autism is to compare the
often diagnosed when a child has major
prevalence of autism among young
problems acquiring spoken language
and old age groups using the same
and as such have a degree of overlap
diagnostic criteria. A real increase should
with the symptoms of autism. Bishop et
be reflected by a higher rate of autism in
al. (2008) found that a number of these
the younger group. A large-scale survey
adults would have been diagnosed with
of autism prevalence rates in the UK by
autism by today’s diagnostic criteria .
the NHS in association with the University
Although the number of people used
of Leicester in 2009 was the first major
4
4
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