Trends in Special Education Code Assignment for Autism: Implications for Prevalence Estimates
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There is considerable controversy over reasons for observed increases in the prevalence of autism spectrum disorders. We examined trends in British Columbia education database coding of children with autism from 1996 to 2004. There was a significant linear increase in autism prevalence. The proportion of children identified by age 6 increased significantly from 1996 to 1999. When we calculated prevalence assuming onset prior to age 3, previously unidentified cases, particularly among girls in 1996 and 1997, accounted for substantial increases in estimated prevalence. The magnitude of under-identification decreased from 1996 to 2000, and rose slightly in 2001. Analyses of prevalence trends must take into account effects of earlier age at identification and inclusion of previously undetected cases on prevalence estimates.
KeywordsAutism autistic disorder prevalence trends special education Edudata Canada British Columbia Ministry of Education
We wish to thank Ms. Nancy Walt, Ms. Caroline Ponsford and Ms. Claudia Roch of the British Columbia Ministry of Education, and Dr. Victor Glickman, Director of Edudata Canada, for providing us with access to the information resources of the British Columbia Ministry of Education through Edudata Canada that were integral to this study. We also wish to thank Ms. Rachel Lomas, a Life Sciences student at Queen’s University, for her assistance with the preparation of this manuscript. We are grateful to the members of the Autism Spectrum Disorders–Canadian-American Research Consortium (ASD-CARC; Jeanette J.A. Holden, principal investigator) for their work on the grant proposal that led to the funding of this and other ASD-CARC projects, and to other members of the ASD-CARC Epidemiology Project team for their contribution to the overall project. Members of these groups are listed on the ASD-CARC’s website at www.autismresearch.ca. This work was supported by a CIHR Interdisciplinary Health Research Team grant (RT-43820) to the ASD-CARC. Dr. Suzanne Lewis sincerely appreciates the support provided by the CIHR Institute of Genetics Clinician Investigator (2003–2005) and Michael Smith Foundation for Health Research Scholar Programs (2005–2010). The findings and interpretations expressed herein are those of the authors, and do not necessarily reflect the opinions of the British Columbia Ministry of Education or of Edudata Canada.
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