Recent worldwide epidemiological surveys of autism conducted in 37 countries are reviewed; the median prevalence of autism is 0.97% in 26 high-income countries. Methodological advances and remaining challenges in designing and executing surveys are discussed, including the effects on prevalence of variable case definitions and nosography, of…

We examined special education classifications among students aged 3-21 in North Carolina public schools, highlighting autism spectrum disorder (ASD) and intellectual disability (ID). Results revealed variability by county in ASD and ID prevalence, and in county-level ratios of ID vs. ASD classifications. Sociodemographic characteristics predicted…

In the last decade, the prevalence of children with autism spectrum disorder (ASD) without intellectual disability (ID) in schools has increased. However, there is a paucity of information on special education placement, service use, and relationships between service use and demographic variables for children with ASD without ID. This study aimed…

The purpose of the present study was to re-examine diagnostic data from a state-wide autism prevalence study (n = 489) conducted in the 1980s to investigate the impact of broader diagnostic criteria on autism spectrum disorder (ASD) case status. Sixty-four (59%) of the 108 originally "Diagnosed Not Autistic" met the current ASD case definition.…

This study examined changes in the administrative prevalence of autism spectrum disorders (ASD) in Utah children from 2002 to 2008 by record source (school and health), age (four, six, and eight), and special education classification. Prevalence increased 100% with 1 in 77 children aged eight identified with ASD by 2008. Across study years and age…

Currently, both the DSM-IV-TR and ICD-10 preclude the diagnosis of Attention Deficit/Hyperactivity Disorder (ADHD) in cases that present with an Autism Spectrum Disorder (ASD). This criterion will be removed in the upcoming DSM-V, but the relationship between ASD and ADHD, and in particular the prevalence of ADHD among the ASD population, remains…

Prevalence statistics for autism spectrum disorders (ASD) vary widely across geographical boundaries. Some variation can be explained by diagnostic methods, case ascertainment and age at diagnosis. This study compared prevalence statistics for two distinct geographical regions, Denmark and Western Australia, both of which have had population-based…

There has been little evidence to support the hypothesis that diagnostic substitution may contribute to increases in the administrative prevalence of autism. We examined trends in assignment of special education codes to British Columbia (BC) school children who had an autism code in at least 1 year between 1996 and 2004, inclusive. The proportion…

Parents or teachers rated 487 non-clinically referred young people with Pervasive Developmental Disorders on the Nisonger Child Behavior Rating Form. The objectives of the study were to examine the relative prevalence of specific behavior problems, assess the impact of subject characteristics, and derive an empirical classification of behavioral…

A study examined the validity of the Gilliam Autism Rating Scale (GARS) with 119 children (ages 3-10) with strict DSM-IV (Diagnostic Statistical Manual of Mental Disorders-IV) diagnoses of autism. The GARS consistently underestimated the likelihood that children would be classified as having autism. Limitations of ratings scales and of the GARS…