THE EVOLUTION OF AUTISM: A BIBLIOMETRIC ANALYSIS OTİZMİN GELİŞİMİ: BİBLİYOMETRİK ANALİZ

Objective: In parallel with the dramatic increase in the autism prevalence, a large number of articles has been published in recent years. The main aim of our study was to make descriptive and evaluative analysis of autism related publications using bibliometric mapping and provide better understanding of autism. Methods: To make the bibliometric analysis of autism literature, all studies published from 1980 to 2020 on autism were selected from Web of Science. Density and network visualization maps according to certain bibliometric indicators (country, source, and keywords) were obtained with VOSviewer software. Results: From 1980 to 2020, 59653 studies on autism were retrieved. The journal publishing the most studies on this subject is Journal of Autism and Developmental Disorders. The countries having the highest number of publications were USA (46.31%), England (11.39%) and Canada (6.02%). The top 3 organization that published most articles about autism were University of California System (3623), University of London (2671) and Harvard University (1663). Conclusion: Studies on autism were on the rise worldwide, especially in the USA. They published in different fields and in many different sources. What needs to be done here is to increase cooperation in work with autism.


Introduction
Autism spectrum disorder (ASD) is a developmental problem with low interpersonal social interaction, repetitive movements and deficiencies in language development. [1][2][3] It was admitted as a comprehensible disorder by Kanner in 1943. 4 While the reasons of ASD have not been determined exactly until now, it was considered that the genetics have a significant effect on it. 5,6 Also the presence of toxins in utero insult during gestation was considered as another possible cause. [6][7][8][9] In the past ASD prevalence was approximately 4 to 5 in 10000 children and it was considered a rare disorder, however, it becomes a common disorder now. 10 ASD prevalence was 1 in 160 in 2019 according to the WHO's data. ASD was seen mostly in Hong Kong with 1 in 27, in South Korea with 1 in 38 and the USA with 1 in 45. 11 It is also seen 4 times higher in boys than girls. 12 Since the criteria for ASD diagnostics changed and awareness about ASD increased over time together with broadening of ASD, an increase was observed in ASD frequency. 13 Although there were several risk factors identified in epidemiological studies, none of them has been proved to be a possible cause of ASD yet. 14 Bibliometrics uses mathematical and statistical methods to make a quantitative evaluation of publication patterns. 15,16 Therefore, it facilitates to understand the written communication process. 16,17 It determines the effective researchers, countries, organizations and their connections and also make the comparisons of them. 16 Bibliometric mapping provides researchers a powerful tool to study the structure and the dynamics of scientific fields and to understand their working field better. 16,18,19,20 With this study, we aim to understand ASD better by conducting the bibliometric analysis of ASD related publications.

Methods
All articles published from 1980 to 2020 on ASD were selected from Web of Science (WoS, Core Collection database maintained by Clarivate Analytics) and analyzed using bibliometric methods. The search keywords were taken as "Autism", "Autistic", "Autism Spectrum Disorder", "ASD" and "Childhood Disintegrative Disorder". The keywords were chosen based on the commonly used definition of ASD. VOSviewer (version 1.6.16) package program was used for bibliometric network visualizations. 21 The following bibliometric indicators were used in this study: 20 • Publication type • Publication language • Country and institutional affiliation • Most productive authors • Source and the name of the journal in which the document was published • Most cited articles According to the h index, the number of citations and publications and also the top ten places in terms of authors, institutions and journals were determined.

Results
Studies on autism have increased significantly in recent years. While approximately 150 studies were published annually in the early 80's, approximately 6000 studies were published in 2020. In this study, a total of 59653 publications were retrieved, 63.69% of which were original articles. The remaining publications were reviews, meeting abstracts, editorial materials, proceedings paper and etc. The primary language was English (96.70%) for the retrieved articles. Other languages like Spanish, French, German, Portuguese, Russian, Turkish and etc. were also encountered.

Country
A total of 160 countries contributed to the advancement of autism research. The top 10 country that published the most articles about autism were USA (46.31%), England (11.39%), Canada (6.02%), Australia (5.23%), Italy (4.12%), France (3.51%), Japan (3.35%), China (3.34%), Netherlands (2.96%) and Germany (2.92%). Of these 160 countries, there were 60 countries that had at least 50 publications. Figure 1 demonstrated the international network visualization of these 60 world countries. The number of publications is given by the size of the circle, the strength of the relationship is indicated by the thickness of the lines and the clusters are shown by the colors. 22

Authors
The top Table 1. Density visualization map of co-authorship for autism research was given in Figure 2. Co-authorship refers to local and international collaborations. People who are away from the set have less co-authorship and collaboration than others. From yellow to blue, more collaborative authors are seen. Moreover top 10 most cited articles according to number of citations per year on autism were given in Table 2.

Discussion
In recent years, there has been a significant increase in the number of cases with autism, from 1 in 2500 cases to 1 in 160. Therefore, serious increases have been observed in the studies conducted in this area. While approximately 200 publications were made annually in the 80s, today this number has reached around 6000. These studies were especially concentrated in the USA. Also, USA is the third country with the most autism cases in the world.
In this study, we analyzed the studies on autism obtained from Web of Science between the years 1980-2020 using bibliometric analysis. Therefore, we aimed to determine the most effective researchers, organizations, countries, journals and their connections. As a result, we found a statistically significant relationship between the number of publications in 10 countries publishing the most on autism and their economic income levels. While less article was done in low-income countries, more article was done in high-income countries. Likewise, Sweileh found a statistically significant relationship between the number of publications of 10 countries publishing the most on autism and the economic levels of them (r=0.948, p<0.01). 15 Journals that contribute more to the literature in terms of number of publications were Journal of Autism and