We investigated the association between selected infant and maternal characteristics and autism risk. Children with autism born in California in 1989-1994 were identified through service agency records and compared with the total population of California live births for selected characteristics recorded on the birth certificate. Multivariate models were used to generate adjusted risk estimates. From a live birth population of more than 3.5 million, 4381 children with autism were identified. Increased risks were observed for males, multiple births, and children born to black mothers. Risk increased as maternal age and maternal education increased. Children born to immigrant mothers had similar or decreased risk compared with California-born mothers. Environmental factors associated with these demographic characteristics may interact with genetic vulnerability to increase the risk of autism. (Croen, L. A., Grether, J. K. & Selvin, S. (2002). Descriptive epidemiology of autism in a California population: Who is at risk? Journal of Autism and Developmental Disorders, 32(3), 217-24.)
The study above shows trends different than studies just released regarding which populations are more vulnerable to autism. African Americans sometimes have increased percentages, sometimes decreased percentages.
I wonder if there are any studies concentrating on how studies are conducted. Are urban populutions approached different than cities, poor from wealthy, school systems with local property taxes providing extra services vs. schools surviving on state and municiple funding?
How closely are autism rates connected to information retrieval protocols?