Statement on Prevalence
Recent press and media reporting has focused on the increasing autism prevalence in the United States. Prevalence is the proportion of a population that is impacted by a disease, disorder, or diagnosis. There are multiple criteria and combinations of criteria to identify or diagnose autism spectrum disorder (ASD). Similarly, there are also many ways to determine prevalence.
The Centers for Disease Control and Prevention (CDC) Autism and Developmental Disabilities Monitoring (ADDM) Network estimates ASD prevalence among the nation’s children, based on a clinical analysis of medical records and, where available, educational records of 8-year-old children from 11 monitoring sites across the United States. In April of 2018, the CDC reported new estimates of the ASD prevalence in the US: 1 in 59 children, an increase of 15% from 1 in 68 in 2016. Learn more about the CDC ADDM Network here: https://www.cdc.gov/ncbddd/autism/addm.html.
In December 2018, two studies were released which reported a higher prevalence of ASD for children in the US, compared to the April 2018 CDC ASD prevalence rate. The increased prevalence was generated from phone surveys of families across the US in 2014, the National Health Interview Survey and the National Survey of Children’s Health,
which asked families to respond, online or by mail, to questions about their children.1 2
Estimating prevalence, or the proportion of a population with a disorder or diagnosis, is best established through surveillance. Surveillance refers to examining the entirety of a population for a disorder or diagnosis. Other methods, like phone surveys, rely upon families who can be reached and who respond. Additional differences, including how data are calculated, what part of the US is studied, researchers’ access or lack of access to types of records, and even how a question is worded can impact prevalence estimates.
The CDC’s ADDM network is the largest population-based surveillance program to monitor ASD and most sites of the ADDM network utilize both health and education records. By using population surveillance and clinical experts who validate the ASD diagnosis, the ADDM network produces a valid estimate of ASD prevalence.
The prevalence of ASD is crucial to making sure that policies and programs can plan for all individuals with an autism spectrum disorder who need services. Advances in diagnosis, interventions and treatments, and appropriate programming across the life span will only benefit from accurate autism prevalence, ultimately leading to a better quality of life for all impacted by ASD.
What is Prevalence
Prevalence is the proportion of people with a diagnosis or disease at a given time. Prevalence is an estimate.
Types of Prevalence
- Point prevalence: prevalence at a given point in time
- Period prevalence: prevalence covering a period of time(like a year)
Prevalence is calculated by comparing the number of people with a certain diagnosis or disease to the number of people in an entire population.
How Can Prevalence Be Measured
Prevalence estimates can be different depending on how people with certain diagnoses and diseases are counted. Here are several ways that prevalence can be measured. Each way has pros and cons.
How Can Prevalence be Measured?
Clinical screening and comprehensive clinical evaluation is the best way to confirm a diagnosis. Professionals, like doctors or clinicians, look at patient records to confirm if a person has a certain diagnosis or disease. Results from clinical evaluation can be reported to the state or city for what’s called a “registry”. Like a census, a registry is a count of the number of people with a diagnosis or disease, not an estimate.
- Information is confirmed by a professional like a researcher or a doctor,not just from a patient or family
- Very accurate
- Requires a lot of people (clinicians, researchers, or doctors) to look at the information and confirm a diagnosis
- People must be willing to share their personal information
- Does not count people who are not added to the registry or seeking services
A census is a count of everyone in a certain population. A census can use different ways to
count people, including phone calls, going to houses, or counting people in a database. A census is meant to be a full count of everyone in a certain population or group, not an estimate.
[Note: The Pennsylvania Autism Census, conducted by the ASERT Collaborative is an “administrative census” which means that it doesn’t count everyone in the population. The PA Autism Census counts only people receiving publicly-funded autism services. For more information visit: paautism.org/census]
- Counts everyone in a population
- Most accurate count
- Very expensive
- Very difficult to count everyone in a population
Federal, state, and local institutions collect a lot of data about health and health services that people use. This information is stored in administrative databases. This method uses data that is already collected to give information about certain diagnoses and diseases.
- Relatively inexpensive
- Data already exists, new collection is not needed
- Large sample sizes
- Long-term observations
- Captures only those people receiving services for specific procedures and diagnoses. It may miss some people
- Information is collected differently, quality may vary
Sometimes, nothing is done to try to know the prevalence of certain diseases and diagnoses.
- No cost
- Impossible to understand the impact a diagnosis or disease has on the population or show the current and future needs
- No guide for future research
- Results in uninformed policy decisions
Surveillance is the continuous collection, analysis, and interpretation of health data used to help plan, implement, and evaluate needs of a population based on estimates. This is specifically designed to track diseases over time to help inform public health action, with the goal of balancing accuracy and cost.
- Design can be flexible depending on the disease or diagnosis
- Primary purpose is to track the disease for which surveillance is constructed
- Time consuming
Surveys ask people questions about their health or diagnoses, and usually are not paired with any other data collection method. Surveys can be an interview, or they can be a paper or electronic form that someone completes on their own. The results of a survey are used to estimate the prevalence of a disease or condition.
- It can be widely spread out to a large amount of people
- There are many ways that surveys can be given (online, in person, by phone, etc.)
- Surveys that rely on individual or family report may not confirm a diagnosis
- How a survey is given may affect who takes a survey (by phone, online, in person, etc.)
- Surveys do not include everyone in the population
Why Does Prevalence Matter
It is important to know about prevalence for many reasons.
- It helps with planning for the needs of the people who have a certain diagnosis or disease.
- Policymakers, administrators, doctors, and service providers need to know how many people need services and treatments so they can plan for the needs right now and the needs in the future.
- Knowing the prevalence also helps researchers who are trying to learn more about certain diagnoses and diseases to see how the population has changed over time.
This information was developed by the Autism Services, Education, Resources, and Training Collaborative (ASERT). For more information, please contact ASERT at 877-231-4244 or info@PAautism.org. ASERT is funded by the Bureau of Supports for Autism and Special Populations, PA Department of Human Services.