The autism epidemic: fact or artifact?

Area of Science:

• Epidemiology
• Developmental Pediatrics
• Public Health

Background:

• Observed increases in the frequency of autistic disorder (AD) over time have raised concerns.
• The role of methodological factors in these reported trends requires careful examination.

Purpose of the Study:

• To illustrate how changes in methodological factors can influence the reported frequency of AD over time.
• To quantify the potential contribution of methodological factors to the observed increase in AD frequency.

Main Methods:

• A prediction analysis was employed to model temporal trends in AD incidence and prevalence.
• The study simulated the impact of broadening diagnostic criteria, earlier age at diagnosis, and improved case ascertainment in a hypothetical population (0-18 years) from 1950 to 2020.

Main Results:

• Conservative changes in methodological factors predicted increases in AD frequency ranging from 2.1- to 28.8-fold.
• Frequency measures by year of birth demonstrated the largest increases.
• While calendar year prevalence and prevalence to age 4 by year of birth were influenced by diagnostic age distribution, 1-year incidence and prevalence to age 12 were not.

Conclusions:

• Methodological factors are likely contributors to the observed increases in AD frequency over time.
• Recommendations are provided for specific frequency measures and study designs to enhance confidence in time trend analyses for AD.