In The Politics of Autism, I discuss evaluation, diagnosis, and the uncertainty of prevalence estimates.
At Autism Research, Jinan Zeidan,Eric Fombonne and colleagues have an article titled "Global prevalence of autism: A systematic review update." Lay abstract:
We reviewed studies of the prevalence of autism worldwide, considering the impact of geographic, ethnic, and socioeconomic factors on prevalence estimates. Approximately 1/100 children are diagnosed with autism spectrum disorder around the world. Prevalence estimates increased over time and varied greatly within and across sociodemographic groups. These findings reflect changes in the definition of autism and differences in the methodology and contexts of prevalence studies.
From the article:
In response to the need for an up-to-date global estimate of ASD prevalence, our review revealed a median prevalence of 65/10,000 as opposed to 62/10,000 in the previous review. In line with previous evidence, recent studies continue to report an increase in measured prevalence over time either at a country level and/or for specific subgroups, for example, the United States (Christensen et al., 2019; Jariwala-Parikh et al., 2019), South Korea (Hong et al., 2020), and Taiwan (Lai et al., 2012). Similarly, an increase in measured prevalence has been reported in later birth cohorts in France (van Bakel et al., 2015) and Australia (May et al., 2020; May et al., 2017; Randall et al., 2016).
Our findings also confirm that the substantial variability observed in the estimates can be, in part, accounted for by methodological and contextual differences among studies. First, surveillance systems, national registries, and other administrative databases offer larger and more representative samples relative to other study designs, but they are usually associated with lower sensitivity for case finding (Dodds et al., 2009), especially in areas with limited availability and/or access to service. In contrast, active case-finding procedures in cohort studies or population-based epidemiological surveys may result in more rigorous estimates, but their results are often confounded by multiple factors related to diverging strategies for case finding, evaluation, and confirmation used across studies. Second, methodological factors also interact with the broader community context where the level of awareness and capacity in health and education systems significantly impact autism identification, evaluation, and therefore prevalence estimates. Third, the evolving nature of the clinical definition of autism and its differentiation from overlapping conditions has continued to influence prevalence estimates.