At the Psychiatric Times (registration free but required), Dr. Allen Frances runs through several familiar explanations for the increase in prevalence (expandining definitions, identification of previously-missed cases, environmental toxins, and changes in diagnostic procedures). He mentions a fifth that has gotten less attention:
There is a systematic bias in all large-scale epidemiological studies to
report as mental disorder even mild presentations of symptoms that may not have
any clinical significance. It is entirely plausible that 3% of the population
might have a smidgen of autism- completely implausible that so many would have
an autistic mental disorder. Rates in epidemiological studies should be seen as
no more than a screening upper limit- not a true reflection of the rate of
actual mental disorder in the population being studied.
Human nature and the true rates of neurological illness and psychiatric
disorder all change very slowly. Environmental toxins are more labile, but
generally don’t just pop out of nowhere to make a condition 100x more common
than it was just 15 short years ago. By far the most plausible explanations for
the autism “epidemic” are factors 1,4, and 5. DSM-IV gave autism purchase by
introducing a milder form close to the populous boundary to normality. Then
autism took flight on the wings of definitional diffusion, Internet contagion,
financial incentive, and naïve interpretation of epidemiological results. The
overall rate of autistic symptoms is probably the same as it always has been
since time immemorial- only the naming of them has changed.
