The Prevalence of Autism Spectrum Disorder in Europe

*Rosemarie Sacco, Nigel Camilleri, Judith Eberhardt, Katja Umla-Runge and Dorothy Newbury-Birch*

#### **Abstract**

This chapter set out to present a comprehensive review on the prevalence of autism spectrum disorder (ASD) among 5–18-year-olds living in Europe. The review was based on studies published between 2015 and 2020. Separate meta-analyses were conducted for population studies and register-based studies to determine the random effects pooled prevalence rate (REPPR) for ASD. The European REPPR for ASD among young people was estimated at 0.8% based on register-based studies and 1.4% based on population. Comparative analysis was carried out to identify trends of prevalence rates across countries, gender, and level of education. The prevalence among primary school children was four times that of secondary school children. A male: female ratio of 3.5:1 was obtained. A range of challenges toward young people with ASD are portrayed, including diagnostic limitations, poor awareness on ASD, and socioeconomic inequality. Nationwide screening, early intervention services, and further research on gender and culture-specific presentations are recommended.

**Keywords:** autism, prevalence, Europe, children, adolescents

### **1. Introduction**

Autism is a neurodevelopmental disorder characterized by persistent and pervasive deficits in social interaction and communication, as well as restricted repetitive behaviors [1]. This definition of autism encapsulates a greater range of presentations when compared with the definition provided by the Diagnostic and Statistical Manual (DSM)-III [2], which listed criteria such as "perversive lack of responsiveness to other people" and "gross deficits in language development." This shift has undoubtedly led to an increase in prevalence rates, ranging from 21 in 10,000 in 1979 [3] to a global figure of 1 in 100 [4] more recently (are there quotes for 1 in 66 too?).

The prevalence is the proportion of individuals in a population with a disease at a specific point in time. This rate is obtained from epidemiological studies such as register-based and population studies. The latter refers to studies that assess all the individuals sampled from a target population to determine the prevalence in that population. On the other hand, register-based studies use registers to determine the number of individuals who are registered with a diagnosis in the target population. Prevalence studies on autism give an indication of the condition's impact in terms of the number of cases, as well as socioeconomical costs. They also indicate the level of awareness, identification, and supportive services offered to the population in question. These data should serve as a foundation from which policymakers plan service development to ensure that the present needs of the population are met [5].

This chapter presents a systematic review on the prevalence of autism among 5–18-year-old young people in Europe. The focus on Europe was intended to obtain a more in-depth understanding among European countries with similar sociodemographic characteristics. Including data from multiple continents may have been interesting to evaluate the entire body of evidence, increase statistical power, and highlight differences in the distribution of autism across different continents. However, adequate clinical and research competence for autism is still developing in low- and middle-income countries [4]. With considerable variation in sociodemographic factors, awareness, and diagnostic expertise [6], there is a risk of prevalence rates being greatly underestimated in certain parts of the world, in fact considerable variation in prevalence rates has been reported across different regions [7, 8]. Crossnational comparisons across countries with very different levels of awareness and expertise on autism may therefore be inappropriate. Furthermore, an overall global prevalence rate may not accurately reflect the situation in Europe.

The review gives a comprehensive appraisal of the eligible prevalence studies, which were published between 2015 and 2020. The short and recent time frame was intended to draw a clearer picture on the current prevalence situation. Previously published meta-analyses have estimated the prevalence of autism by including studies dating back to 1966 [8]. While including studies from the distant past may improve the statistical power, the pooled prevalence rates may not be generalized to the current situation and not reflect the reported rise in prevalence over time [4]. Moreover, the chapter presents cross-national comparisons of prevalence rates to ascertain trends across countries, gender, and level of education. These were used to draw inferences on present barriers to identification of autism, such as stigma, poor diagnostic systems, and unequal diagnostic sensitivity across gender and age. Methodological and diagnostic factors that may under- or overestimate the true prevalence of autism are also discussed.
