Bibliometric analysis of research themes and trends in childhood autism spectrum disorders from 2012 to 2021

Background Autism spectrum disorders (ASD) are heterogeneous neurodevelopmental conditions that affect people worldwide. Early diagnosis and clinical support help achieve good outcomes. However, medical system structure and restricted resource availability create challenges that increase the risk of poor outcomes. Understanding the research progress of childhood ASD in recent years, based on clinical literature reports, can give relevant researchers and rehabilitation therapists more resonable research guides. Objective This bibliometric study aimed to summarize themes and trends in research on childhood ASD and to suggest directions for future enquiry. Methods Citations were downloaded from the Web of Science Core Collection database on childhood ASD published from 1 January 2012, to 31 December 2021. The retrieved information was analyzed using CiteSpace.5.8. R3, and VOS viewer. Results A total of 7,611 papers were published across 103 areas. The United States was the leading source of publications. The clusters that have continued into 2020 include coronavirus disease 2019, gut microbiota, and physical activity, which represent key research topics. Keywords with frequency spikes during 2018–2021 were “disabilities monitoring network,” “United States,” and “caregiver.” Conclusions The Autism and Developmental Disabilities Monitoring Network in the United States can be used as a reference for relevant workers worldwide. An intelligent medical assistant system is being developed. Further studies are required to elucidate challenges associated with caring for a child with ASD.


Introduction
Autism spectrum disorders (ASD) are heterogeneous neurodevelopmental conditions, characterized by early-onset difficulties in communication and restricted, repetitive behavior and interests (1). In 2020, the World Health Organization reported that 1 in 160 children worldwide presents with ASD (2). The United States National Center for Health Statistics reported in 2016 that the prevalence of ASD among children aged 3 to 17 years is 1 in 45 and that it is increasing, which is a cause for concern. ASD is a lifelong neurodevelopmental disorder with a profound impact on intellectual and general abilities and psychological functioning (3,4). ASD was first described based on the characteristics of 11 children observed by child psychiatrist Kanner in 1943 (5). The definition of ASD continues to evolve (1,(6)(7)(8). The understanding of ASD is also evolving, and the number of related studies is increasing. Examining what currently constitutes research frontiers may help set directions for future research (9). This study aimed to examine the current evidence on childhood ASD, including research trends and leading topics, published over the past decade, and to propose directions for future research. These findings may be used as a reference for epidemiologists, pediatricians, rehabilitation therapists, and caregivers.
This study aimed to cover the following aspects. We analyzed Science Citation Index for childhood ASD studies using bibliometric methods. Countries, regions, institutions, and periodicals of study origin, study categories, keywords, and references per study were included in the dataset. Visual representation of findings was provided. Research influence of countries, regions, institutions, and journals was examined, and leading research topics were reported. We went over the hot spot trend in greater depth.

Materials and methods
On 24 March 2022, all citations published between 1 January 2012, and 31 December 2021, were retrieved from the Web of Science Core Collection (WoSCC). The search strategy was set as TI = ("autistic * " OR "autism * " OR "ASD" OR "Kanner * " OR "Autism spectrum disorder") AND TI = (children OR Kid * ), the document type was "ARTICLE, " and the timeframe was from 1 January 2012 to 31 December 2021. A total of 8,160 papers were retrieved. After manual screening, 7,611 articles were included, and data on the following variables were extracted: title, publication year, country or region, institution, journal, references, and keywords ( Figure 1).

Statistical analysis
Citation features were analyzed using CiteSpace.5.8. R3 and VOSviewer. The H-index was used to estimate the importance or impact of citations obtained from WoSCC.

Annual distribution of publications
Both the retrieval result analyzer of Web of Science database and the duplicate removal function of CiteSpace software can obtain the number of documents issued each year. Over the past 10 years, the number of studies on childhood ASD has increased ( Figure 2). The number of publications in this area increased from 2011 to 2018. More than 1,000 research papers were published in this area from 2018 to 2020. Finally, from 2020 to 2021, the number of documents decreased slightly.

Countries or regions
Using the country cooperation analysis function of CiteSpace, we can get the number of countries that have published articles and the influence of articles from a country. A total of 7,611 papers were published in 103 countries or regions. Collaborations among countries/regions are shown in Figure 3. The number of publications corresponds to the size of tags or nodes. Centrality can be ascertained from the purple ring area. Regions with the greatest number of citations included the United States (n = 3,655), Britain (n = 653), Australia (n = 553), China (n = 478), and Canada (n = 472). Among them, the United States (0.40) and Britain (0.17) have purple rings, representing articles from these regions have been cited more frequently than articles from other countries ( Table 1). The H-index represents citation influence. The three countries with the highest h-index are the United States (102), England (58) and Canada (50).

Institutions
The cooperation between institutions and the number of published articles of each institution can be achieved through CiteSpace software. Table 2 lists the top ten institutions with the largest number of documents, and their partnerships are shown in Figure 4. Eight of them are located in the United States, one in Canada, and one in the United Kingdom. The total link strength shows the influence of each institution.

Journals and research category
Using VOSviewer to analyze the citation source journals and co cited journals. The documents in the highest citing journals represent leading research topics. The research field of highly  cited journals are research basic knowledge. Tables 3, 4 show the top ten citing journals and cited journals, respectively. The leading research fields included psychology, special education, psychiatry, rehabilitation medicine, behavioral science, rehabilitation medicine, genetics, and neuroscience. Areas cited at increased frequencies included psychology, psychiatry, special education, rehabilitation medicine pediatrics, and behavioral science. The Journal of Autism and Developmental Disorders emerged as the most influential journal in this field ( Figure 5).

Keywords
The default setting of CiteSpace is changed to the following mode: "Year Per Slice" = 2, "Top N%" = 30.0%, and "Minimum Duration" = 2. Figure 6 summarizes the leading keywords, including the year of emergence. The red square in Figure 6 represents emerging keywords for the investigated timeline. The most frequently used keywords were "spectrum" (

References
Using the default setting of CiteSpace to cluster the co cited documents and choose label clusters with indexing terms.
. /fpubh. .   The clustering labels of co-cited articles depend on citing and cited journals. The cited studies constitute knowledge base of research. The frequency of reference use represents its influence. Co-citations reveal research themes and development background. Table 5 lists the top 10 cited studies, which include research of diagnostic criteria, intervention methods, epidemiological findings, and ASD characteristics. Two of these studies examined ASD within families. The clustering labels of cited documents are obtained from the citing documents. Figure 7 presents clusters that continued into 2020, including #2 COVID-19, #4 gut microbiota, and #5 physical activity.

Principal results
The number of studies on childhood ASD has increased likely due to a combination of educational and medical system  changes, which increased disease awareness. The number of published studies decreased from 2020 to 2021 likely due to restrictions associated with the coronavirus disease 2019 pandemic. The United States is the leading source of studies, suggesting policies and regulations in this country are more responsive to the needs of autism patients than those in other countries. The most influential journal in this field is the Journal of Autism and Developmental Disorders. This field includes disciplines such as psychology, psychiatry, special education, rehabilitation, medicine, pediatrics, and behavioral science. Meanwhile, keyword co-occurrence and reference cluster analysis revealed changes in research focus over time.
From the emerging keywords from 2012 to 2015, the diagnosis of ASD and its comorbidity were the research hotspots of that year.
In 2016 and 2017, we tend to establish randomized controlled trials within ASD groups and the differences between ASD and typical development groups. Based on previous research findings, researchers began looking for more appropriate technologies to establish disability monitoring networks and strengthen attention to ASD caregivers from 2017 to 2021.

FIGURE
The cooperation of citiation journals that contributed to publications on Childhood ASD from to . that more than half of the United States' counties lack a Board Certified Behavior Analyst (BCBA) qualified to provide behavioral and psychological assessments and interventions due to differences in reimbursement ratios (28). This finding suggests that many children with ASD do not receive the required support. The research on the prevalence monitoring of autism is still worthy of attention. Disability monitoring networks are an essential source of research data and clinical guidance, informing research and treatment strategies, and helping improve patient outcomes. This relies on scientific diagnostic tools.

Caregivers
Research into caregivers of children with ASD covers aspects such as caregiver demographic characteristics and views on treatment, nursing training, and health problem, quality of life, and family cohesion surveys, as well as input into specialist nursing and intelligent care system development.
Demographic characteristics of patients, caregivers, and communities affect the perception of patients with ASD. The mothers of 396 children from Singapore completed a quantitative checklist for autism in adults, revealing that child sex, cognitive function, birth order, mother age, and ethnicity were not characteristics of autism reported by caregivers. Delayed or impaired language development in the child and depressive symptoms and low education level in the mother were associated with social autism (29). Caregivers able to predict child problematic behavior may take action to minimize this risk. However, such predictions are challenging for caregivers that do not receive BCBA support, in which case the use of artificial intelligence technologies may be useful. Zheng et al. proposed a machine learning-based framework that helps predict problem behavior (30). Following an early diagnosis, caregivers of children with ASD need specialist education Frontiers in Public Health frontiersin.org . /fpubh. .

FIGURE
Timeline of publication co-citations on childhood ASD from to .
to help meet child needs. This approach also encourages social interaction among caregivers (31), which helps improve caregiver physical and psychological health and quality of life (32,33). In 2021, Nie et al. proposed an immersive interaction system based on augmented reality to help autistic children practice social attention skills (34).

Limitations
There are some limitations to this study. First, we downloaded only citations from the WoSCC database. The findings may differ if citations from other databases are included. Second, despite efforts to reduce bias in this study, no study method can reduce bias present in the original studies. Third, this study only included research findings published between 2012 and 2021. Some relevant studies are on-going, precluding inclusion in the present study, which may subject these results to the effects of time lag. Some of the most recent research hotspots require manual reading to be discovered. The use of artificial intelligence in medicine is increasing, providing novel opportunities to codify existing bias and change practice (35); the use of these technologies in ASD research and care is particularly promising (36).

Conclusions
Disability monitoring networks and caregiver-focused questions are the leading areas of research in childhood ASD, aiming to improve diagnosis, interventions, and outcomes. Many questions in this field remain unanswered. Eleven sites across the United States provide ASD prevalence data, which may support policy development and clinical practice. These data may help establish rehabilitation intervention systems for caregivers, supporting disease management. The use of artificial intelligence-based technologies may support research and clinical practice, including studies aimed at elucidating neurobiomarkers of ASD. Remote assessment and intervention guidance is required in the time of pandemics (37,38).

Data availability statement
The original contributions presented in the study are included in the article/supplementary files, further inquiries can be directed to the corresponding author.
Author contributions JZ, YL, and FZ acquired, analyzed the data, and drafted the manuscript. FF, XD, and XingW analyzed the data. MW and XiaoW designed the research, acquired the article information, and revised the manuscript. All authors agreed to be accountable for the content of the work. All authors contributed to the article and approved the submitted version.

Funding
The work was financially supported the Key R&D and Promotion Projects in Henan Province (222102310615) and Henan Province Medical Science and Technology