This is a commonly asked question, and the public and media conclusion seems to be: Yes.  These complex conditions are now being diagnosed far more often than ever before.  Does this suggest these disorders are becoming more and more common?  Or could it be we health care and educational professionals simply have not diagnosed these conditions in the past?

I will call your attention now to a brilliantly conceived and important British study published one month ago in Archives of General Psychiatry, Vol. 68, (NO. 5) May 2011: "Epidemiology of Autism Spectrum Disorders in Adults in the Community in England,"  by Dr. Traolach S. Brugha, et al. {There are eight other authors, all from respected British universities.}  The article may be found on pages 459-466.

SUMMARY OF STUDY METHODS:  This was part of the 3rd national study of psychiatric morbidity * of adults in England in 2007.  Participants were adults (16 and older) in the general community.  7461 adults completed phase 1 interviews, and of these 618 completed phase 2 diagnostic assessments.  Study subjects were screened using the Autism-Spectrum Quotient (AQ) in phase 1, and then the subjects selected for phase 2 were given the Autism Diagnostic Observation Schedule, Module 4 (ADOS-4).  A diagnosis of the adult having an Autism Spectrum condition required 4 well-qualified interviewers achieving at least 90% agreement.

RESULTS:  There was no significant difference in the prevalence of an Autism Spectrum Disorder (ASD) related to age.  This study claims to demonstrate for the first time in the general community population that the rate of incidence of ASD is not significantly related to age, suggesting the causes of autism are temporally constant.**

*  "Morbidity" as used here means a form of pathology, as in any illness or condition.
**  "Temporally Constant" is an awkward way of saying the rates do not change with time, as in        aging.

IN EFFECT there was no evidence ASD is more prevalent now than one or two or more generations in the past.  Contrary to some public and media stories, ASD incidence is NOT increasing; it appears we are now simply much more astute in diagnosing theses problems in children, adolescents, and a few adults.  Asperger's Disorder was first entered into the lexicon of Psychiatry when DSM-IV was published in 1994.  The overwhelming majority of adults found to have an ASD diagnosis in this study were diagnosed with Asperger's Disorder or "High Functioning Autism."  None had ever been diagnosed with ASD in the past. Their social, emotional, and (often) cognitive problems simply had gone unnoticed.

These conclusions are also strongly compatible with other studies which have shown an overall 1% prevalence rate of ASD in the general population.  This is also the same rate found in the last three published large studies of children 15 and under.  Two of those three studies used the same diagnostic protocol as used in this survey, i.e., the ADOS-4.

One of the findings of this research is slightly at odds with rrelativley recent data published by the (American) Center for Disease Control (CDC).  Reports from that facility - to the best of my recall - have indicated an ASD occurs in about 1.3 - 1.5% of boys and 0.3 - 0.5% of girls.  This study found an ASD condition in 18.2 men / 1000, or about 1.8% of boys, but only 2 / 1000, or 0.2% in adult women.

These researchers also found a very small % of ASD-diagnosed individuals were or had ever been married.  The ASD adults were alos in a lower than average income level than the general population studied, and had a lower level of educational success.  They were also far more foten "renters" of their housing instead of being "owners" compared to other community members.

CONCLUDING COMMENTS:  In my opinion, this exhaustive and important study should end the public and media debate about any truly increasing incidence of ASD conditions.  Like ADHD, it is simply far more commonly recognized and diagnosed now compared to past generations.

The authors have obviously recognized the distressing nature of their rather dismal adult outcome data, and offer possible explanations.  They note (p. 461) having started with 13,171 households identified as potentially eligible for study, but were only able to complete phase 1 assessments of 7461 adults, a response rate of only 56.6%.  4075 people refused to participate.  Of the 849 adults selected for phase 2 interviews, 62 refused and for various reasons no contact could be made with 157, leaving 630 eligible for full phase 2 interviews; of these 618 were able to complete the assessments.  They "lost" an awful lot of adults whose responses might have at least slightly altered the outcome data.

Educators and mental health professionals of all disciplines who have worked with ASD-affected children and adults certaily are more than well aware of the many difficulties we routinely encounter even in less rigorous assessment procedures.

Further, although the authors mention most of the adults had Asperger's Disorder or "High Functioning Autism," they do not further distinguish the numbers of characteristics of other study subjects.  It would not take a great many severely afflicted full-blown autistic adults to "skew" these data, just like we so often see in otherwise seemingly bright and capable 7th grade kids:  They can score well on most tests and turn in most assignments, but a grade of Zero in 5-10% of homework they failed to turn in can drag their grade down from a B to a D or F very quickly indeed.

Corydon G. Clark, M.D.