Why can autism spectrum disorder prevalence estimates differ between countries?

Prevalence estimates for autism spectrum disorder (ASD) vary significantly between countries due to several key factors:

• Diagnostic Criteria: The use of broader or narrower clinical definitions impacts how many individuals are identified. The transition to a single diagnosis under the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) is one example of how classification changes affect reported numbers.1
• Resources and Surveillance: Differences in available healthcare resources and the specific surveillance methods used to track cases—such as changes in survey questions—can lead to variations in reported prevalence.1
• Awareness and Screening: Improved screening tools and increased public awareness contribute to higher diagnosis rates, which may be more prevalent in certain regions than others.2

Because of these variables, it remains difficult to determine if reported increases in incidence reflect a true rise in the condition or simply improved clinical recognition and reporting practices.1