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I'm now turning to the issue of the trends
over time in prevalence and their interpretation.
So the interest of examining time trends is to assess
whether or not the increase in the prevalence of autism over
the years really means that there is an epidemic of autism,
and by that we mean an increase in the incidence of the condition in the population,
or could it simply reflect a change in the diagnostic concepts and
criteria and better ways to ascertain cases in surveys?
In this slide, which comes from one state of the US, Minnesota,
we just portrayed the Department of Education data showing that in 1990-1991,
there has been a very progressive,
regular increase in the number of cases of autism reported in the school system.
That kind of trend has been shown in many countries
or many states in the US when you look at data
from such sources like
the Department of Education or other kinds of administrative databases.
If one looks at the history of nosography at the same time,
there has been a major change in
the conceptualization of autism occurring during those years.
So in 1987, for instance,
DSM-III-R was the nosographic system in place,
which was replaced in '92 and '94 by both ICD-10 and DSM-IV, particularly in the US,
and these two nosographies really embodied new concepts of autism,
a broader view of the condition,
and also dimensionization of the phenotype,
which was new, which was showing that autism was
incorporating children who had mild phenotypes,
children who had language well-developed,
and a normal cognitive functioning.
So the increase in the rates of autism mapped with this change in nosography.
In the US, in addition to that,
in 1990, there was a major change in the legislation,
which required that autism would now be
reported as a separate special disability category in the US,
whereas before that, it was actually not identified as a separate condition.
Of course, that meant that there was a huge interest for autism,
new services were developed for it,
new supportive measures were implemented in the early intervention systems.
So all that change in social policies meant that autism now was looked after,
was screened for, and new services were put in
place to support the development of children with this condition.
As a result of that,
more diagnosis were provided both in
the medical system and certainly in the school system as well.