Trends in the prevalence of autism on the basis of special education data.
OBJECTIVE
The goal was to determine whether the increasing prevalence of autism, on the basis of educational data, in Wisconsin between 2002 and 2008 was uniform in all school districts or was greatest in districts with lower baseline (2002) prevalence.


METHODS
Special education counts were obtained for all Wisconsin elementary school districts from 2002 through 2008. The annual prevalence of children being served under the autism category was calculated for each district, districts were grouped into 8 categories (octiles) according to their baseline prevalence, and prevalence trends were plotted according to octile.


RESULTS
The overall prevalence of use of the autism category in Wisconsin elementary schools increased from 4.9 to 9.0 cases per 1000 children between 2002 and 2008. The magnitude of this increase was not uniform across districts and was inversely associated with baseline prevalence. Prevalence in the lowest octile increased from 0.5 cases per 1000 students in 2002 to 7.0 cases per 1000 students in 2008 (P < .0001), whereas no significant trend was seen for the octile with the highest baseline prevalence (range: 11.2-12.3 cases per 1000 students; P = .11). The highest-octile/lowest-octile prevalence ratio decreased from 24.6 (95% confidence interval: 16.2-37.3) in 2002 to 1.8 (95% confidence interval: 1.6-2.1) in 2008.


CONCLUSIONS
The prevalence of use of the autism special education category in Wisconsin seems to be leveling off in the school districts with the highest prevalence rates, at ∼12 cases per 1000 students, whereas the gap in prevalence between districts overall has narrowed.
Department of Population Health Sciences, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53705, USA. mjmaenner@wisc.edu
Matthew J
MJ
Maenner
Maureen S
MS
Durkin
D001321:Autistic Disorder / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy; D002648:Child; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D004519:Education, Special / Q000706:statistics & numerical data*; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D011203:Poverty / Q000706:statistics & numerical data; D012959:Socioeconomic Factors; D014922:Wisconsin