The University of Minnesota was funded by the Centers for Disease Control and Prevention (CDC) to conduct a multi-source public health project that monitors the prevalence of autism spectrum disorder (ASD) and intellectual disability in 8-year-old children within Hennepin and Ramsey counties in Minnesota.
In addition to race and ethnicity categories routinely studied by the CDC, the Minnesota-Autism and Developmental Disabilities Monitoring Network (MN-ADDM) project was interested in understanding prevalence among Somali and Hmong immigrant populations. The data was collected from health and special education records of children who were 8 years old in 2014.
- Using data from 2014, MN-ADDM researchers found 1 in 42 (2.4%) 8-year-old children was identified with ASD. This percentage is higher than the average percentage identified with ASD (1.7% - 1 in 59) within all communities in the United States where the CDC tracked ASD in 2014.
- Boys were more likely to be identified with ASD than girls.
- There were no significant statistical differences in prevalence by racial and ethnic groups. The prevalence estimate was 1 in 26 for Somali children and 1 in 54 for Hmong children. Although both of these numbers look different from the 1 in 42 estimate, sample sizes were too small to be able to tell if these differences are real or occurred by random chance. Using a p-value of <.01, there were no statistically significant differences across race and ethnicity. Additionally, the confidence intervals around the prevalence estimates are large, and this tells us we should use extreme caution before drawing conclusions about any differences between groups.
- There were no significant statistical differences in prevalence between white, black, and Hispanic children.
- Among children identified with ASD who had IQ information available, less than a third (28%) also had intellectual disability.
- Intelligence quotient (IQ) scores were available for 80% of children identified with ASD by MN-ADDM. Intellectual disability is defined as IQ score ≤ 70.
- When we looked at ethnic groups, of the Somali children with ASD who had IQ information available, 43% also had a co-occurring intellectual disability and 18% of Hmong children with ASD also had intellectual disability.
- About 73% of children identified with ASD had concerns about their development noted in their health and/or education records by age 3.
- About 34% of children identified with ASD received a comprehensive developmental evaluation by age 3.
- Even though ASD can be diagnosed as early as age 2, about half of children were not diagnosed with ASD by a community provider until 4 years and 9 months.
- Autism spectrum disorder
Autism spectrum disorder (ASD) is a developmental disability that is caused by differences in how the brain functions. People with ASD may communicate, interact, behave, and learn in different ways. Signs of ASD begin during early childhood and usually last throughout a person’s life (1). ASD includes former diagnoses of autistic disorder, pervasive developmental disorder, not otherwise specified (PDD-NOS), and Asperger disorder. These diagnoses were collapsed into the single category of ASD in 2013.
- Confidence interval
A confidence interval gives an estimated range of values which is likely to include the information (e.g., prevalence) that we want to know about. The interval is a range of values that you can have confidence contains the true value in the population. There are different levels of confidence intervals; the most common is 95%. With a 95% confidence interval, we say that we are 95% confident that the value in our population will be included in our interval. 5% of the time, it will not. So, we could say, “We are 95% confident that the prevalence of ASD in 8-year-olds in our surveillance area was between 21 and 27 per 1,000 children in 2014. Larger samples typically have smaller confidence intervals. Smaller samples usually have bigger confidence intervals.
- Intellectual disability
Intellectual disability means that a person has difficulty learning at an expected level and functioning in daily life. In this report, intellectual disability is measured by intellectual quotient (IQ) test scores of less than or equal to 70.
Prevalence is a scientific term that describes the number of people with a disease or condition among a defined group at a specific period in time. Prevalence is usually expressed as a percentage or proportion of the defined group. For this project, we counted the number of 8-year-olds in 2014 who were identified with ASD and then divided that number by the total number of 8-year-olds in our surveillance area during 2014.