Are Low Functioning Autism Subjects Excluded From Autism Research?

How often do you see studies or reports about low functioning autism? It appears that research about "autism" is skewed towards research of high functioning autism and Aspergers as in the above notice requesting research participants for an Ontario autism study. If research is focused exclusively, or almost exclusively, on participants with high functioning autism or Aspergers how much do we really know about Autistic Disorder which, by definition, includes those with low functioning autism?

I entered the words "functioning autism" into the Google Scholar search bar. The first 3 pages, the first 30 entries, all referred to high functioning autism. 2 out of the 30 results referred to low functioning autism in connection with high functioning autism. None of the results referred solely to low functioning autism. Entry of the term high functioning autism in the Google Scholar search bar produced 56,800 results. Entry of the words low functioning autism produced 44,900 results.

I am not suggesting that such searches are probative, scientific or thorough. But they leave me with an impression that autism research tends to be skewed toward high functioning Autism (and Aspergers) and tends to exclude low functioning autistic subjects. If anyone knows of any surveys of the professional literature that have been done which might confirm or refute this impression I would be interested in reading them.

autism