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The global prevalence of autism spectrum disorder in children: a systematic review and meta-analysis

Article information

Osong Public Health Res Perspect. 2025;16(1):3-27
Publication date (electronic) : 2025 February 10
doi : https://doi.org/10.24171/j.phrp.2024.0286
Alwin Issac1orcid_icon, Kurvatteppa Halemani,2orcid_icon, Asha Shetty1orcid_icon, Latha Thimmappa3orcid_icon, VR Vijay2orcid_icon, Kiranmayi Koni2orcid_icon, Prabhaker Mishra4orcid_icon, Vishwas Kapoor4orcid_icon
1College of Nursing, All India Institute of Medical Sciences, Bhubaneswar, India
2College of Nursing, All India Institute of Medical Sciences, Raebareli, India
3College of Nursing, All India Institute of Medical Sciences, Kalyani, India
4Department of Biostatistics & Health Informatics, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, India
Corresponding author: Kurvatteppa Halemani Room No 124, first floor, Medical College Building, College of Nursing, All India Institute of Medical Sciences (AIIMS), Raebareli, Uttar Pradesh 229405, India E-mail: kurru.hali@gmail.com
Received 2024 October 12; Revised 2024 December 28; Accepted 2025 January 6.

Abstract

Objectives

The objective of this review was to analyze quantitative data on autism spectrum disorder (ASD) and to increase the accuracy of estimates of the prevalence of ASD.

Methods

This review, which was reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement, included studies conducted from January 2008 to June 2024 on children aged 3 to 18 years that used standardized measurement tools and reported cut-off scores for ASD. The prevalence of ASD was the primary outcome analyzed in this review. The PubMed, Clinical Key, Scopus, Embase, CINAHL, and Web of Science databases were reviewed for relevant studies. The review protocol was registered with PROSPERO and followed the Cochrane collaboration guidelines.

Results

A total of 66 studies reported on the prevalence of ASD, screening 21,313,061 children worldwide. Among these, 25 studies were conducted in Europe, 22 in Asia, and 13 in America. Additionally, 3 studies each were reported from Africa and Australia. According to a meta-analysis, 0.77% of children globally are diagnosed with ASD, with boys comprising 1.14% of this group. Notably, Australia showed the highest prevalence rate, with an effect size of 2.18, highlighting it as a critical area for public health focus.

Conclusion

ASD represents a significant global health burden. Early detection, increased awareness among parents, and prompt intervention are crucial for mitigating developmental problems in children later in life. It is essential for health policymakers to acknowledge the prevalence and growing trends of ASD in order to implement effective interventions.

Keywords: Autism spectrum disorder; Child; Mental disorders; Neurodevelopmental disorders; Prevalence

Graphical abstract

Introduction

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder characterized by difficulties in social relationships and repetitive or restricted behaviors [1]. The spectrum encompasses various disorders, including autistic disorder, Rett disorder, Asperger syndrome, and pervasive developmental disorder [2]. Its prevalence is increasing worldwide, presenting significant challenges for affected individuals and their families [3]. The World Health Organization estimates that autism affects 0.76% of children globally, with higher incidence rates in developed countries [4]. Autism can be diagnosed as early as 18 to 24 months, as its symptoms often become distinguishable from typical development and other developmental delays during this period. Changes in diagnostic criteria have contributed to an increase in reported cases, along with heightened public awareness and understanding of ASD [5]. Environmental assessments and genetic testing play critical roles in identifying risk factors and enhancing predictions of ASD [6,7]. Together, these elements are driving the increased prevalence of ASD in developed countries [7].

Over the past 50 years, ASD has transformed from a narrowly defined, rare childhood condition into a widely recognized, researched, and advocated lifelong disorder. It is now understood to be common and highly heterogeneous. While the core features—social communication deficits and repetitive or unusual sensory-motor behaviors—remain largely unchanged [8], autism is now viewed as a spectrum that ranges from mild to severe. Many individuals with ASD require lifelong support, although this is not the case for everyone. ASD remains one of the top neurodevelopmental disorders among children. The first case of ASD was reported in 1943, and since then, the number of cases has increased worldwide. According to epidemiological data, the prevalence of ASD in the United States of America (USA) is reported to be 18.5 per 1,000 children under 8 years of age. The majority of countries have reported an increase in the number of ASD cases over the past decades [9]. Although South Asia accounts for over 20% of the global population, the prevalence of ASD is underreported there [10].

The Centers for Disease Control and Prevention reports that 1 in 54 children in the USA was diagnosed with ASD from 2014 to 2016 [11]. In Italy, the prevalence among 7- to 9-year-olds is 1.15% [12]. During the 1960s and 1970s, ASD rates ranged from 0.5 to 0.7 cases per 10,000 people. More recently, the Autism and Developmental Disabilities Monitoring Network found prevalence rates of 67 to 230 cases per 10,000, reflecting a 243% increase in the USA [13]. The revised Diagnostic and Statistical Manual of Mental Disorders, 5th Edition, Text Revision (DSM-5-TR) (2022) criteria require a higher threshold of clinical symptoms compared to the DSM, 4th Edition, Text Revision (DSM-IV-TR) criteria, enhancing the accuracy of ASD diagnoses among children [14,15]. Variations in diagnostic criteria and parental awareness may influence these prevalence rates. Early detection, standardized diagnostic criteria, counseling, awareness of ASD, and a safe environment can improve the reporting of ASD [16].

The updated DSM-5, improves diagnostic accuracy, particularly for cases that were previously undiagnosed [17]. In the USA, the estimated cost of autism, at 268.3 billion US dollars (USD), exceeds that of stroke and hypertension. The annual costs vary from 1.4 to 2.4 million USD. If current trends persist, these costs are projected to increase to between 11.5 trillion and 15 trillion USD by 2029 [18].

Thus, early diagnosis and intervention are crucial to reduce the financial burdens of this condition. An updated estimate assists health professionals in formulating public health strategies. Accurately estimating the prevalence of autism is crucial for assessing the economic burden and allocating adequate resources and services for individuals with autism and their families. Additionally, determining prevalence helps identify vulnerable groups and associated geographical and environmental risk factors [19]. While previous meta-analyses have focused on ASD prevalence in the general population and reported cumulative results [13], our study specifically targets children and includes subgroup analyses based on sex and the income levels of countries. This review aims to provide a comprehensive pooled estimate of global ASD prevalence among children.

Materials and Methods

Eligibility Criteria

This systematic review and meta-analysis aimed to determine the pooled global prevalence of ASD in children. The review protocol was registered with PROSPERO (CRD42023445469), adhered to Cochrane collaboration guidelines [20], and was reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [21]. The review included studies on children aged 3 to 18 years that utilized standardized measurement tools and provided cut-off scores for ASD. It considered original studies published in the English language from January 1, 2008, to June 31, 2024, that reported on the prevalence of ASD in children. Publications in non-English languages were excluded due to their limited impact and small sample sizes. Additionally, the results from these studies could not be validated by official authorities. Qualitative studies, case reports, and studies lacking prevalence data were also excluded. The primary outcome analyzed in this systematic review and meta-analysis was the prevalence of ASD.

Information Sources

A systematic review and meta-analysis were conducted by searching PubMed, ClinicalKey, Scopus, Embase, CINAHL, and Web of Science for studies published from January 1, 2008, to June 31, 2024.

Search Strategy

The search included terms such as “autism spectrum disorder,” “prevalence,” “autism,” “autism spectrum disorders,” “child development disorder,” “deprived child,” “pervasive developmental disorders,” “children,” “infant,” “toddler,” “school age,” “adolescence,” “cross-sectional study,” “observational study,” and “cohort study.” Two authors (K.H. and A.I.) independently conducted searches on PubMed, ClinicalKey, Scopus, Embase, CINAHL, and Web of Science.

A comprehensive search strategy was developed using keywords and Medical Subject Heading (MeSH) terms related to population, intervention, comparator, and outcomes in Medline, and this strategy was adapted for use in other databases. The identified articles were imported into Rayyan software, where duplicates were eliminated using the “check for duplicates” tool [22]. The citations and references of relevant articles that met the inclusion criteria were manually searched to identify additional studies. All remaining original full-text articles were then screened according to the inclusion criteria.

Selection Process

A data extraction sheet was developed to gather information from the included studies. Two reviewers (K.H. and A.I.) independently extracted the data, which was subsequently reviewed by a third reviewer (A.S.). The extraction form captured several details, including the authors, publication year, country, study design, sample size, participant characteristics, tools used, and key findings as reported by the authors.

Data Collection Process

Two independent authors (K.H. and A.I.) conducted the data extraction procedure, while a third reviewer verified the accuracy of the retrieved data. The figures and tables that summarize and report the extracted data are available in Table S1.

Study Risk of Bias Assessment

The methodological quality and risk of bias in the articles were evaluated using a modified Newcastle-Ottawa scale (NOS). This scale ranges from 1 to 5, where 1 is the lowest and 5 is the highest possible score. A higher score indicates better study quality, which typically suggests a lower risk of bias. The scale is particularly suited for assessing the quality of non-experimental studies, including observational, cohort, and retrospective studies. The quality assessment encompasses 5 criteria: sample representativeness, sample size, response rate, measurement tools and cut-off scores, and statistical details. Each criterion contributes 1 point to the total score, with studies achieving a score above 3 considered to be at low risk.

Effect Measures

The pooled data from individual studies were manually entered and coded in Microsoft Excel (Microsoft Corp.) before being transferred to Stata software ver. 17 (Stata Corp LP). We assessed heterogeneity among the studies using the I² test, categorizing values as high (>75%), medium (50%–75%), and low (<50%) [23]. Due to the observed heterogeneity, a random effects model was employed. The effect size (ES) was calculated, along with 95% confidence intervals (CIs), using the Metaprop and Metan commands. We conducted subgroup analysis based on geographical differences in the prevalence of ASD.

Synthesis Methods

Various subgroup analyses were initially planned for the retrieved data. However, the data demonstrated insufficient information and subtle differences between children and adults. As a result, we were unable to conduct a meta-analysis among the adult population. Consequently, this systematic review and meta-analysis included descriptive studies, and the pooled data were presented in dichotomous form.

Results

Study Selection

The search yielded 26,849 studies from online databases and an additional 4 from printed sources. After eliminating 4,514 duplicates, 21,987 articles were excluded for failing to meet the review criteria. We assessed 348 full-text articles, of which 88 and 194 were further excluded due to various issues, including difference in primary outcome, other illness, missing sample sizes and measurement tools, unspecified cut-off scores, inclusion of participants with other illnesses, and differences in primary outcomes. Ultimately, 66 articles were included in the meta-analysis. A flow diagram of the study selection process is depicted in Figure 1.

Figure 1.

Flow diagram of study selection. a)The PubMed, Clinical Key, Scopus, Embase, CINAHL, and Web of Science. b)Excluded after title and abstract screening.

Study Characteristics

This systematic review and meta-analysis encompassed a total of 21.31 million children screened for ASD. A global compilation of 66 studies reported on the prevalence of ASD among children. Of these, 25 studies were conducted in Europe [12,24–47], 22 in Asia [48–68], and 13 in America [69–81]. Additionally, 3 studies each were reported from Africa [68,82,83] and Australia [84–86]. Among these studies, 25 articles specifically reported the prevalence of ASD among boys (Table 1) [12,24,27–29,37,44,46,49–53,56–58,60,61,63,67,70,84,86–88].

Characteristics of the included studies

Further, 47 studies were reported from high-income countries [12,24–47,56,62,65,66,69–80,84–87,89,90], 16 studies from middle-income countries [48–55,57–59,61,63,64,67,88], and 3 studies from low-income countries (Table 1) [68,82,83].

The sample sizes in the included trials ranged from 374 [59] to 6,900,000 [35], with participant ages varying from 1 to 18 years. The primary outcome of these studies was the prevalence of autism. Various instruments were employed to measure this prevalence, including the modified checklist for autism in toddlers (CHAT), social communication questionnaire (SCQ), Indian scale for assessment of autism (ISAA), DSM-IV, International Classification of Disease (ICD-9), autism diagnostic observation schedule (ADOS), DSM-5, strengths and difficulties questionnaire (SDQ), Qatar School survey (QSS), and autism diagnostic interview-revised (Table 2) [12,24–53,55–79,81–90].

Quality appraisal of the included studies using the modified Newcastle-Ottawa scale

Results of Individual Studies

Prevalence of ASD in different geographical regions

The use of more sophisticated diagnostic criteria may increase the prevalence rates. Many countries do not maintain statistical data on ASD; therefore, cases may only be recognized when a child visits the hospital for other health issues. Symptoms can range from mild to severe, and many children improve and lead normal lives. The meta-analysis found that 0.77% of children worldwide were diagnosed with ASD (ES, 0.77; 95% CI, 0.52–0.86; p=0.001; I2=97.5%). Among the continents, Australia had the highest prevalence of ASD in children (ES, 2.18; 95% CI, 0.08–4.28; p=0.001; I2=99.3%), followed by Africa (ES, 1.51; 95% CI, 0.28–2.74; p=0.001; I2=98.2%) [68,82,83], America (ES, 1.10; 95% CI, 0.79–1.41; p=0.00; I2=98.9%) [69–81], Europe (ES, 0.71; 95% CI, 0.54–0.88; p=0.001; I2=97.5%) [12,24–47], and Asia (ES, 0.28; 95% CI, 0.19–0.38; p=0.001; I2=99.7%) (Figure 2) [48–68].

Figure 2.

Global prevalence of autism spectrum disorder by continent. CI, confidence interval.

Prevalence of ASD in boys

A meta-analysis was conducted of 25 studies that reported the prevalence of ASD in boys. Most primary studies indicated that the prevalence in boys was 2 to 3 times higher than that in girls. This meta-analysis found that 1.14% of children worldwide were diagnosed with ASD (ES, 1.14; 95% CI, 0.61–1.67; p=0.00; I2=99.9%) (Figure 3) [12,24,27–29,37,44,46,49–53,56–68,70,84,86–88].

Figure 3.

Prevalence of autism spectrum disorder among boys. CI, confidence interval.

The prevalence of ASD among children in low middle- and high-income countries

According to the World Bank, countries are classified as high-income, middle-income, or low-income. Based on 47 studies with relevant data reported that 0.86% of ASD cases were from high-income countries (ES, 0.86; 95% CI, 0.66–1.06; p=0.00; I2=99.9%) [12,24–47,56,62,65,66,69–80,84–87,89,90]. Among these, 2 studies reported notably higher prevalence rates: 3.6% in Sweden [44] and 4.2% in Australia [84] (Figure 4).

Figure 4.

Prevalence of autism spectrum disorder in high-income countries. CI, confidence interval.

Similarly, 16 studies reported a prevalence of ASD in middle-income countries (ES, 0.30; 95% CI, 0.17–0.43; p=0.00; I2=99.4%) [48–55,57–59,61,63,64,67,88]. Three studies reported prevalence of ASD from low-income countries (ES, 1.5; 95% CI, 0.28–2.74; p=0.00; I2=99.4%) (Figure 5) [68,82,83].

Figure 5.

Prevalence of autism in middle- and low-income countries. CI, confidence interval.

Developed countries have focused more on health infrastructure and services. In contrast, low- and middle-income countries face challenges such as inadequate knowledge of diagnostic tools, poor healthcare infrastructure, and a lack of trained medical professionals. Additionally, these countries experience a scarcity of research studies. Cultural values and traditional practices also contribute to disparities in access to healthcare facilities [91].

Heterogeneity of included studies

The Galbraith plot is a graphical representation that illustrates study-specific ESs and their precisions, as well as the overall ES, and detects potential outliers. The plot features 2 horizontal lines: the green line, which represents the reference line indicating no effect, and the red line, which is the regression line. The slope of the red line reflects the overall ES and the standardized log risk ratio for each study. Circles below the green line indicate an increased risk. However, no studies were reported below the reference line (green line) in this analysis. The present meta-analysis revealed that most circles were found within the shaded region, except for 3 studies, suggesting that these studies appeared within the 95% CI. The Galbraith plot concluded that 3 out of the 66 studies fell outside the shaded region, indicating considerable heterogeneity after employing a random effect model among the ESs in the present meta-analysis. Heterogeneity and publication bias are reported in Figures 6 and 7.

Figure 6.

Heterogeneity of the included studies. CI, confidence interval.

Figure 7.

Publication bias. CI, confidence interval.

Discussion

This updated systematic review and meta-analysis estimated the global prevalence of ASD over the past decade. The adoption of standardized diagnostic criteria and assessment tools has led to an increase in reported ASD cases worldwide. Additionally, improved screening and community surveillance have improved detection at the peripheral level [92,93]. Although previous studies have explored the diagnosis and occurrence of ASD [94], there is still a lack of evidence concerning its identification and management. A meta-analysis indicates that perinatal and postnatal factors could increase the risk of ASD, although the specific risk factors are inconsistent. Genetic factors play a significant role, as the presence of siblings with autism increases the incidence [94]. Environmental factors, including exposure to various drugs and chemicals, may also contribute to the risk of ASD [95–97].

The findings of this systematic review and meta-analysis provide significant insights into the global prevalence of ASD among children, with a substantial sample size exceeding 21 million. The meta-analysis incorporated data from 66 studies spanning various continents, revealing geographical disparities in ASD prevalence rates. Notably, Australia showed the highest prevalence rate, with an ES of 2.18, marking it as a critical area for public health focus [98]. In contrast, the lowest prevalence was recorded in Asia, with an ES of 0.34, which may reflect differences in diagnostic practices or reporting mechanisms [99].

The data also highlighted that the prevalence of ASD is notably higher in boys, with an ES of 1.14, suggesting a male-to-female ratio ranging from 2:1 to 3:1 across various studies [36,100]. This finding aligns with previous research indicating a disparity between the sexes in ASD diagnoses, warranting further investigation into the biological and environmental factors that may contribute to this difference.

The analysis further categorized studies by income level, revealing that high-income countries reported an ASD prevalence of 0.86% (ES, 0.86), with Sweden and Australia showing particularly elevated rates (3.6% and 4.2%, respectively). This suggests that higher-income countries may have better resources and screening practices, leading to more accurate diagnoses. In contrast, middle-income countries reported a lower prevalence of 0.30%, indicating potential underdiagnoses or differences in healthcare access and awareness [13,101].

The reported prevalence of anxiety in low-income countries is alarmingly high [102], highlighting concerns about the availability of mental health resources in these areas. This variation in prevalence across different income levels underscores the importance of designing interventions that are tailored to specific socioeconomic contexts.

The significant heterogeneity observed in the included studies, with I² values frequently exceeding 97%, underscores the difficulties in comparing findings across diverse populations and methodologies. This variability could be attributed to differences in diagnostic criteria, cultural perceptions of ASD, and the structures of health systems. Many countries do not have comprehensive statistical data on ASD and often only identify cases during healthcare visits for unrelated issues.

Culture, race, and ethnicity play a significant role in the neuropsychological development of children and affect early diagnosis and treatment. Healthcare professionals must consider the cultural backgrounds and customs of families, which in turn helps them understand perceptions of healthcare services. Due to social stigma, parents may hesitate to disclose their child’s symptoms. Therefore, understanding cultural perceptions is a crucial component in diagnosing ASD [103–105].

The prevalence of ASD has increasingly garnered global attention. However, assessing its occurrence poses challenges due to the absence of national data in many regions. Some nations have begun to officially recognize ASD as a disability, providing valuable data that aids in calculating and categorizing its prevalence across different ages, genders, and geographical locations. In contrast, many countries still fail to report local and national ASD data. Previous research has indicated that phenotypic characteristics, environmental factors, and gender differences contribute to a higher incidence of ASD in boys than in girls [106,107]. Nevertheless, further experimental studies are necessary to accurately determine the risk factors associated with different genders and geographical regions.

According to the Australian National Disability Insurance Agency, the annual cost of ASD is projected to increase by 100 billion USD by 2032. The prevalence of ASD in Australia is similar to that in Japan, where early diagnosis and timely interventions contribute to higher reported numbers. Additionally, several studies indicate that changes in diagnostic criteria and increased awareness of ASDs have resulted in more people receiving diagnoses. However, some clinicians have been confusing the diagnosis of ASD with attention deficit hyperactivity disorder and dyslexia. Moreover, government policies, particularly the National Disability Insurance Scheme, play a crucial role in encouraging more reporting of ASD cases in Australia. The current study revealed that the prevalence of ASD in Australia is higher among boys, but the reason for this disparity remains unclear [108–112].

Overall, the findings of this meta-analysis not only contribute to the existing literature on ASD prevalence but also underscore the need for increased global awareness, improved diagnostic practices, and targeted public health initiatives, especially in underrepresented regions and low-resource settings. As our global understanding of ASD continues to evolve, further research is crucial to navigate the complexities of diagnosis, support, and treatment for affected children and their families.

Conclusion

The recent increase in ASD prevalence is concerning, particularly in developing countries where accurate estimates are essential for devising effective public health strategies. Early diagnosis and intervention can significantly enhance outcomes for children with ASD. However, it remains uncertain whether this rise indicates true trends or merely reflects changes in diagnostic criteria. Future research should utilize consistent methodologies, as many existing studies are not accessible due to language barriers. Moreover, the absence of prevalence data in some countries highlights the urgent need for further research to improve ASD management globally.

HIGHLIGHTS

• This systematic review and meta-analysis investigated autism spectrum disorder (ASD), a chronic neurodevelopmental disorder that is increasing dramatically worldwide, posing significant challenges for healthcare workers, patients, and their families.

• Many countries, particularly low and middle-income nations, lack sufficient data on ASD. The global prevalence of ASD has been reported at 0.77%, with rates being higher among males at 1.14 per 100 children.

• High-income countries had an ASD prevalence of 0.86%. Notably, Sweden and Australia exhibited significantly higher rates, at 3.6% and 4.2%, respectively.

• Low and middle-income countries exhibited a lower prevalence of 0.30%, suggesting potential underdiagnoses or differences in healthcare access and awareness as possible explanations.

• The identification of mental disorders in children is often neglected and overlooked, potentially increasing the risk of mental health burdens and long-term psychiatric disorders in the future. Therefore, it is crucial to develop policies that address the psychological needs of both children and adults.

Supplementary Material

Supplementary data are available at https://doi.org/10.24171/j.phrp.2024.0286.

Table S1.

Search strategy.

j-phrp-2024-0286-Supplementary-Table-1.pdf

Notes

Ethics Approval

This is a review study registered with PROSPERO (CRD42023445469), and available online.

Conflicts of Interest

The authors have no conflicts of interest to declare.

Funding

None.

Availability of Data

The datasets are not publicly available but are available from the corresponding author upon reasonable request.

Authors’ Contributions

Conceptualization: KH, AI; Data curation: AS, LT, VRV; Formal analysis: PM, VK; Investigation: KH, AS, IC; Methodology: KH, KK, PM; Project administration: AS, LT; Resources: AI, KK; Software: PM, VK; Supervision: AS; Validation: PM, LT; Visualization: AS, KK; Writing–original draft: KH, AI; Writing–review & editing: all authors. All authors read and approved the final manuscript.

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Article information Continued

© 2025 Korea Disease Control and Prevention Agency.

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Figure 1.

Figure 1.

Flow diagram of study selection. a)The PubMed, Clinical Key, Scopus, Embase, CINAHL, and Web of Science. b)Excluded after title and abstract screening.

Figure 2.

Figure 2.

Global prevalence of autism spectrum disorder by continent. CI, confidence interval.

Figure 3.

Figure 3.

Prevalence of autism spectrum disorder among boys. CI, confidence interval.

Figure 4.

Figure 4.

Prevalence of autism spectrum disorder in high-income countries. CI, confidence interval.

Figure 5.

Figure 5.

Prevalence of autism in middle- and low-income countries. CI, confidence interval.

Figure 6.

Figure 6.

Heterogeneity of the included studies. CI, confidence interval.

Figure 7.

Figure 7.

Publication bias. CI, confidence interval.

Table 1.

Characteristics of the included studies

Study Published year Country Research design Sample size Age (y) Inclusion Tool/criteria Findings
Asia
 Akhter et al. [50] 2018 Bangladesh Cross-sectional T, 5,286; M, 3,436; F, 1,850 1.5–3 Information was gathered from household data on the rural population of Bangladesh. CHAT The study found that 0.075% of children were diagnosed with ASD in rural areas of Bangladesh.
 Heys et al. [48] 2018 Nepal Cross-sectional 4,098 9–13 The parents of children under 18 years of age residing in rural areas, with a known history of developmental delay, were considered. Autism quotient-10 The study revealed that 14 students scored more than 6 out of 10, indicating that the tool used in the study could be adopted in Nepal. The study also showed that the sensitivity and specificity of the scale yielded consistent results.
 Raina et al [49] 2017 India Cross-sectional T, 28,070; M, 14,019; F, 14,051 1–10 Children with poor cognitive development were included from tribal, rural, and urban areas. ISAA ASD was reported to be 2 times higher in rural areas and 3.2 times more prevalent in boys. A total of 0.15% of children were reported to have ASD.
 Rudra et al. [51] 2017 India Cross-sectional T, 5,947; M, 3,344; F, 2,603 3–8 The data were obtained from teachers and parents of students attending special disability schools in Kolkata. SCDC, SCQ, ADOS In eastern India, 0.23% of children were reported to have ASD, with teachers rating children higher than parents did.
 Chaaya et al. [52] 2016 Lebanon Cross-sectional T, 998; M, 537; F, 462 1.3–4 Data were collected from syndicate nurseries in Lebanon. M-CHAT Approximately 1.53% of children were diagnosed with autism. Further studies are recommended with a larger sample size.
 Huang et al. [53] 2014 China Cross-sectional T, 8,000; M, 537; F, 7,463 1.5–3 The cases were identified based on the DSM-IV criteria checklist for children from urban and rural areas. CHAT mixed The prevalence of ASD was higher in boys compared to girls. Compared to western countries, ASD incidence was lower. Social stigma and lack of awareness were major contributing factors.
 Raz et al. [89] 2015 Israel Survey study T, 2,431,649; M, 1,247,552; F, 118,097 8 ASD cases were identified through computerized records from hospitals and official Israeli websites. DSM The study revealed that 0.37% of children experienced autism. The findings highlight areas for government facilities to improve.
 Poovathinal et al. [63] 2016 India Community-based survey T, 18,480; M, 9,132; F, 9,348 1–3 Structured questionnaires were used to gather data from primary health workers in both rural and urban areas. DSM ASD was reported in 23.3 per 10,000 children aged 6 to 10 years and 16 to 20 years, with the majority of cases previously undiagnosed.
 Raina et al. [55] 2015 India Cross-sectional T, 11,000; M, 9,132; F, 5,757 1–10 The data collection was conducted in 2 stages: the first stage involved assessing children using an indigenous autism scale, and the second stage involved evaluating autism symptoms. ISAA The results showed that 0.9% of children were reported to have ASD. Socioeconomic status was a significant factor influencing ASD prevalence.
 Chien et al. [57] 2011 Taiwan Survey study T, 372,642; M, 185,420; F, 187,222 17 Data obtained from the national database were used to examine the prevalence and incidence of ASD. DSM mixed The prevalence of ASD increased from 1.79 to 28.72 per 10,000 between 1996 and 2005, with annual incidence rising from 0.91 to 4.41 per 10,000. The prevalence was higher among boys aged 0 to 5 years.
 Kim et al. [58] 2011 China, Korea Longitudinal study T, 22,660; M, 11,679; F, 10,981 7–12 Cases identified from disability schools were considered for further evaluation of ASD. ASSQ, ADOS, ADI‑R The study found that two-thirds of the cases were undiagnosed and untreated. The authors emphasized the importance of timely screening for better detection, assessment, and treatment of ASD.
 Perera et al. [59] 2009 Sri Lanka Cross-sectional T, 374 1.5–2 Children were identified from registers maintained by Primary Health Centers, and all eligible children were further screened for ASD. M‑CHAT About 7.4% of children showed red flags for ASD. High prevalence was detected through community-based screening, but there is a need to develop culturally sensitive screening tools.
 Sun et al. [60] 2015 China Survey study T, 714; M, 371; F, 343 1.5–2 Cases were identified through the official records of the Beijing China Disabled Persons' Federation, a state-run special rehabilitation center, and ASD-approved hospitals. CAST, ADOS, ADI‑R The majority of children (119 per 10,000) were undiagnosed with ASD, underscoring the need for further screening using appropriate diagnostic methods. Similar rates were reported in developed nations.
 Al-Farsi et al. [87] 2011 Oman Cross-sectional T, 798,913; M, 412,675; F, 386,238 1–14 Children were screened for autism using standardized scales, including DSM-IV-TR criteria, and all participants came from rural and urban communities in Oman. CARS The overall prevalence of ASD was 1.4%, with more than 75% of cases reported in boys from low-income families. Poor diagnosis and unrecognized cases contributed to the low numbers reported in Oman.
 Li et al. [64] 2011 China Survey study 616,940 0–17 Cases were also identified by systematically evaluating family histories of ASD from the China National Sample Survey on Disability. DSM-5 The study revealed that untrained or inadequately trained professionals and poor knowledge of ASD among healthcare workers led to poor diagnosis, increasing the number of undiagnosed cases. These findings can help in planning interventions.
 Al-Mamri et al. [65] 2019 Oman Retrospective study T, 837,655 0–14 Data were retrieved from the 3 main autism diagnostic centers in Oman: Sultan Qaboos University Hospital, Royal Hospital, and Al-Massarah Hospital. Identified cases were referred to these diagnostic centers. DSM-5 Between 2012 and 2018, 20.35 per 10,000 children were diagnosed with ASD, with boys 3.4 times more likely to be affected than girls. Compared to the prevalence in 2011, the ASD rate was 15 times higher, indicating improvements in screening and diagnostic criteria.
 Alshaban et al. [66] 2019 Qatar Survey study T, 9,074; M, 3,716; F, 5,358 5–12 The data collection involved 2 phases: in the first phase, children were identified through screening, and in the second phase, those who met the initial criteria underwent further evaluation. QSS-SCQ A total of 844 ASD cases were identified, with most children having language issues, including word articulation (75.1%) and phrase speech (91.4%). Pre- and perinatal risk factors contributing to neurodevelopment were also identified.
 Zhou et al. [67] 2020 China Survey study T, 125,806; M, 66,687; F, 59,119 6–12 Cases were selected from the Public Security Bureau Household Registration System, with data collected from both regular and special disability schools in China. DSM-IV TR The overall prevalence of ASD was 0.29%, with most cases reported in boys. Many of the children attended regular schools and led normal lives. Of the children with ASD, 90.4% had more than 1 neuropsychiatric comorbidity.
 Sun et al. [88] 2019 China Survey study T, 7,167; M, 3,282; F, 3,885 6–10 Children were selected based on median economic levels, with all information sourced from the National Statistics in Mainland China. DS M-I V TR The study found that 77 cases of ASD were reported among 72,697 children, accounting for 97 out of every 10,000 children with ASD. Similar findings were reported in western China.
 Jin et al. [61] 2018 China Survey study T, 72,697 3–12 Cases were also identified from special education schools. Data were collected in 2 stages: first, parents and teachers were invited to screen children using the SCQ (Social Communication Questionnaire). SCQ The study revealed that 8.3 per 10,000 children were likely to be diagnosed with ASD. Most diagnosed children had an IQ below 40, and many ASD cases were previously undiagnosed.
 Al-Zahrani [62] 2013 USA Cross-sectional T, 22,950 7–12 The sample was recruited by screening and assessing children from regular schools. Parents and teachers were invited to screen children using the ASSQ, and those scoring above 10 were considered positive. DSM, ASSQ The overall prevalence of autism was 0.035% among a sample population of 22,950 students, with ASD more frequently reported in males (0.031%) than females (0.004%). Counseling and education for parents and teachers were found to aid in appropriate management.
America
 van Balkom et al. [40] 2009 Island Survey study T, 13,109 0–9 Cases were identified through the screening of official records, using data from previous studies and children’s psychiatry hospitals in Aruba. DSM‑IV The study revealed that 1.9 out of every 1,000 children had autistic disorders, and 5.3 per 1,000 were diagnosed with ASD. Samples were identified from the Centers for Educational and Counseling Support.
 Nicholas et al. [69] 2009 USA Survey study/Cohort study T, 8,156 4 Children with autism were identified through records and community-based screenings. The data were categorized by region and compared with other relevant information. DS M-I V TR The study revealed that 8.0 in 1,000 children were diagnosed with ASD. Previous data indicated that 7.6 in 1,000 children were diagnosed in 2000, and 7.0 in 1,000 children in 2002, within the same geographical region.
 Kogan et al. [70] 2018 USA Survey study T, 43,283 3–17 The data were collected from the United States Centers for Disease Control and Prevention and the ADDM Network. Further evaluations were conducted to ensure the accuracy of ASD diagnoses. DSM-IV-TR The majority of children received symptomatic treatment, with 27% undergoing treatment specifically for ASD and 64% receiving behavioral therapy. However, the prevalence of ASD, reported as 1 in 40 children, varied based on income and social background.
 Baio et al. [71] 2018 USA Survey study T, 325,483 8 Samples were identified through the ADDM Network, and families or parents residing near ADDM sites were included. Data collection was conducted at 11 selected sites. DSM-IV-TR The overall prevalence of ASD ranged from 13.1 to 29.3 per 1,000 children. The study also found that boys were diagnosed with ASD more often than girls, particularly among non-Hispanic White children.
 Christensen et al. [79] 2016 USA Survey study T, 346,978 8 Data were obtained from official records maintained by US authorities. Additionally, detailed screening was performed for those who scored above the normal range. DSM-IV-TR The prevalence of ASD was higher among 8-year-old boys than girls of the same age. Non-Hispanic White children had a higher prevalence of ASD than non-Hispanic Black children, with an overall estimated prevalence of 14.6 per 1,000.
 Durkin et al. [73] 2017 USA Cross-sectional T, 1,308,641; M, 668,575; F, 640,066 8 Cases were identified from special disability schools, followed by further screening in the second stage to confirm the accuracy of the autism diagnoses. DSM-IV-TR The study identified a significant association between ASD and racial demographics. Diagnosis rates varied along a socioeconomic status gradient between 2002 and 2010.
 Fombonne et al. [74] 2016 Mexico Survey study T, 4,195 8 ASD cases were identified in medical and educational institutions, including special disability schools, and evaluated by qualified professionals. LASI The study revealed that 0.87% of children (80.6% male) were diagnosed with ASD. One-fourth of the children had intellectual disabilities, and 69% exhibited behavioral issues.
 Nicholas et al. [75] 2008 USA Survey study T, 47,726 8 Cases were identified through hospital records, and further evaluations were conducted to assess the severity of ASD from 2000 to 2015. Each case was linked to 1 of the specified ASD diagnosis codes. DSM-IV-TR In South Carolina, ASD affected 1 in 162 children aged 8. The study projected that the number of cases may increase over time.
 Diallo et al. [76] 2018 USA Survey study T, 1,447,660 1–17 Samples were recruited from Spanish-speaking schools in the metropolitan district of Quito. ICD-10, ICD-9 The prevalence of ASD increased by approximately 1.2% from 2014 to 2015. This finding supports the need for medical services to adapt to the evolving requirements of patients and families.
 Dekkers et al. [77] 2015 Ecuador Survey study T, 51,453 5–15 Cases were identified from a specialized hospital in Maracaibo County, with participants screened using standard autism diagnostic criteria. DSM‑III The study reported an overall ASD prevalence of 0.11%, with 0.21% suspected cases. However, this low prevalence suggests that many children with ASD are not included in regular education.
 Montiel-Nava and Pena [78] 2008 Venezuela Cross-sectional T, 254,905 3–9 Data collection occurred in 2 phases: the first phase involved gathering clinical information in a community setting, and the second phase referred cases for systematic ASD examinations. ADOS The study revealed that 1.7 per 1,000 children were diagnosed with ASD, highlighting the need for health and education authorities to reassess services provided to children.
 Christensen et al. [72] 2019 USA Survey study T, 363,749 8 The study included children residing in specific areas during 2020. Cases from special disability schools were also considered. DSM‑IV‑TR, ICD‑9 The prevalence was 18.5 per 1,000 among 8-year-old children, with ASD being 4.3 times more common in boys. Prevalence rates were similar for non-Hispanic White, non-Hispanic Black, and Asian/Pacific Islander children but lower for Hispanic children.
 Shaw et al. [81] 2023 USA Survey study T, 72,277 4 Cases were identified through community medical and educational services. Children with neurodevelopmental delays were referred to higher centers for further screening. DSM‑IV‑TR, ICD‑9 The study found that ASD prevalence was higher in boys and 1.8 times higher in Hispanic children, 1.6 times in non-Hispanic Black children, and 1.4 times in Asian children. The majority of children had intellectual and memory difficulties.
 Maenner et al. [90] 2020 USA Survey study T, 275,419 8 Children with autism were identified through records and community-based screenings. The data were categorized by region and compared with other relevant information. DSM‑IV The study revealed that 27.6% of 8-year-old children were diagnosed with ASD, with prevalence 3.8 times higher in males. ASD was most commonly seen in non-Hispanic White children (24.3%) and non-Hispanic American Indian children (26.5%). It was also prevalent among children from low socioeconomic backgrounds.
Africa
 Lagunju et al. [68] 2014 Nigeria Cohort study T, 2,320 3.9 The samples were recruited from the pediatric neurology and child psychiatry clinic of University College Hospital and screened for autistic disorder. DSM‑IV The study revealed that the majority of cases were identified during the study period, with 2.3% (2,320) new ASD cases diagnosed in children. Most of these children had neurodevelopmental comorbidities.
 Zeglam and Maound [82] 2012 Libya Cross-sectional T, 38,508 0–16 Cases were identified between 2005 and 2009 and screened for language and behavioral difficulties at the Neurodevelopment Clinic of Al-Khadra Hospital in Tripoli. DSM‑IV The study found that ASD prevalence was 4 times higher in boys than in girls. The cases were commonly reported in children between the ages of 2 and 5 years, with the majority diagnosed 6–28 months after the onset of symptoms.
 Hewitt et al. [83] 2016 Somalia Cross-sectional T, 12,329; M, 6,163; F, 6,166 7–9 Samples were recruited through household screenings. Following this, clinical examinations were conducted, and positive cases were referred for further evaluation. DSM‑IV The study emphasized the importance of screening positive for both ASD and other neurodevelopmental conditions. It recommended conducting neurodevelopmental assessments alongside ASD screenings.
Europe
 Kocovska et al. [24] 2012 Faroe Islands Longitudinal study T, 7,128; M, 3,590; F, 3,538 15–24 Cases were identified through mass screening conducted from 2002 to 2009 in the Faroe Islands. ASSQ, ADOS The study revealed that cases of ASD increased from 0.56% in 2002 to 0.94% in 2009, with a comparatively limited range.
 Nygren et al. [25] 2012 Sweden Survey study T, 5,007 2 Samples were recruited from 2-year-old children, and suspected cases were referred for detailed screening. These children underwent further evaluation at higher centers. M‑CHAT The findings indicated that 0.8% of children were diagnosed with ASD. Mass screening using a standardized scale improved the accuracy of ASD diagnoses in children.
 Morales-Hidalgo et al. [26] 2018 Spain Survey study T, 2,765 4–11 The study included participants under 11 years of age, with ASD screening performed by school teachers and parents using a standardized autism scale. ADOS, ADI‑R The study showed that 1.5% of children were diagnosed with ASD at age 4, while 1% were diagnosed between the ages of 6 and 11 years. Boys were diagnosed with ASD at a 4:1 ratio compared to girls.
 Fernell and Gillberg [27] 2010 Sweden Cohort T, 24,084; M, 12,342; F, 11,742 6 Cases were identified through clinical assessments and follow-up care, which included screening for cognitive and functional development in children. ADOS About 6.2 out of every 1,000 children were diagnosed with ASD, and one-third of these children led normal lives without cognitive or language problems.
 Skonieczna-Zydecka et al. [28] 2017 Poland Survey study T, 707,975; M, 344,506; F, 3,63,469 0–16 Data were collected from government registries, including Provincial Disability Services Commissions. ADOS, Q‑CHA The results revealed that ASD prevalence was 4 times higher in boys, with 35 out of every 10,000 children diagnosed.
 Idring et al. [29] 2015 Sweden Cohort T, 735,096; M, 376,617; F, 3,58,479 0–27 Samples were identified using official records maintained in Sweden. ICD‑10 The study reviewed the increasing prevalence of ASD due to screening and awareness programs.
 Davidovitch et al. [56] 2013 Israel Cross-sectional study T, 423,524; M, 218,076; F, 205,448 1–12 Data from Israeli health organizations were used to estimate the occurrence of ASD in children under 12 years old. DSM The results showed that approximately 0.48% of children are prone to ASD, with many cases reported in 8-year-old children. Differences in incidence rates were noted between Israel and the US.
 Saemundsen et al. [30] 2013 Iceland Cohort T, 22,229; M, 11,424; F, 10,805 1–15 Cases were identified from hospital records, and suspected cases underwent further evaluation for medical conditions and chromosomal abnormalities after clinical diagnosis. ADOS, ADI‑R The prevalence of all ASD types was 120.1 per 10,000, with 172.4 per 10,000 for boys and 64.8 per 10,000 for girls. Early diagnosis and intervention improved reporting of ASD cases.
 Posserud et al. [31] 2010 Norway Survey study T, 6,609 7–9 Children scoring above the 95th percentile were further screened, and parents or teachers were asked to complete the ASSQ for additional diagnosis. ASSQ, DAWBA, DISCO The prevalence of ASD increased from 0.72% to 0.87%. The study emphasized the need to assess cases and implement social awareness programs.
 Isaksen et al. [32] 2012 Norway Survey study T:31,015 12 Samples were identified from special disability schools, with additional information gathered from healthcare records maintained by local health centers. ADOS ADI‑R The prevalence of ASD increased 10-fold. Recent findings significantly influence policymakers to establish improved diagnostic and management criteria for ASD.
 Mattila et al. [33] 2011 Finland Survey study T, 4,422 8 Cases were identified by systematically assessing children’s activities in schools, using standardized ASD diagnostic criteria administered by trained personnel. ASSQ, ADOS, ADI‑R, FSIQ The prevalence of ASDs was 8.4 per 1,000, and autism alone was 4.1 per 1,000. Most children with ASD had low IQs, cognitive dysfunctions, or other chromosomal and high-functioning disorders.
 van Bakel et al. [34] 2015 France Survey study T, 307,751 7 Cases were identified through official records maintained by the French authorities. The average age of the children was 7 years, and the study was conducted between 1997 and 2003. ICD-10 Approximately 36.5 per 10,000 children were diagnosed with ASD, the majority of whom were male (4:1 ratio). Nearly 47.3% of these children had intellectual disabilities.
 Narzisi et al. [12] 2018 Italy Survey study T, 10,138; M, 5,231; F, 4,907 7–9 Autism cases were identified by medical practitioners and verified by the ASDEU team. In the next stage, teachers and children completed the ASD diagnostic form. DSM‑5, SCQ The majority of ASD cases went undiagnosed until mass screenings were conducted. About 1% of new cases were identified during these screenings.
 Bachmann et al. [35] 2018 Germany Survey study T, 6,900,000 0–24 Samples were identified from health records maintained by the outpatient department of the nationwide health insurance fund. ICD‑10 The study revealed that the prevalence of ASD was unclear. Developed countries showed higher prevalence rates due to poor diagnosis or inadequate ASD screening.
 Baron-Cohen et al. [36] 2009 UK Survey study T, 11,700 5–9 Cases were obtained from the Special Educational Needs register, and children were invited for detailed examinations with the help of their parents. CAST, ADOS ADI‑R The study found that 11 children were diagnosed with ASD after screening. An estimated 157 per 10,000 children were diagnosed, highlighting the need for planning and implementing new policies.
 Hansen et al. [37] 2015 Denmark Survey study T, 677,915 0–20 Cases were identified in official health authority records in Denmark. Children were continuously screened from birth until their ASD diagnosis. ICD‑8, ICD‑10 The study reported that 33% of children diagnosed with ASD could be attributed to new diagnostic criteria, which improved ASD screening and intervention.
 Parner et al. [38] 2008 Denmark Cohort study T, 407,458 0–11 Cases were retrieved from the Danish Medical Birth Registry and the Danish National Psychiatric Register, with all participants screened using a standardized ASD scale. ICD‑10 The majority of ASD cases were reported in young children. The study emphasized that ASD can be diagnosed in younger children over time. Accurate screening with appropriate tools could reduce the incidence of ASD.
 Thomaidis et al. [39] 2020 Greece Population-based cohort study T, 182,879; M, 93,897; F, 88,982 10–11 Samples were identified from the Centers for Educational and Counseling Support, which were directly linked to special educational support schools. ICD‑1 The study found that 1.15% of children had ASD, with a higher prevalence in males (4:1 ratio). By age 4, 3.8% of children had been diagnosed, and 42.7% were diagnosed before age 6, with a mean age of diagnosis at 6.1 years.
 Suren et al. [41] 2012 Norway Survey study T, 731,318 0–11 Autism cases were identified from the Norwegian Patient Register, an official document maintained by the Norwegian healthcare authority. DSM‑IV The study reported that 0.7% of children had ASD, with a higher prevalence in males (4.3:1 ratio). ASD significantly impacted neurodevelopmental milestones, especially in 11-year-old children.
 Fuentes et al. [42] 2021 Spain Survey study T, 14,734 7–9 Cases of autism were identified through a community survey involving a two-stage screening process: the first stage consisted of the community survey, and the second stage involved screening by teachers and parents. ADOS, ADI‑R, SCQ The study showed that 0.59% of children were diagnosed with ASD, which was lower than in previous studies. Due to its cross-sectional nature, further longitudinal studies are recommended to better understand ASD prevalence.
 Boilson et al. [43] 2016 Ireland Survey study T, 5,589 6–11 Samples were identified using standardized autism screening formats to diagnose children across Europe. SCQ Screening for ASD was implemented using the EAIS protocol, which employed the Social Communication Questionnaire as a first-level screening tool in Irish national schools.
 Linnsand et al. [44] 2021 Sweden Survey study T, 902; M, 454; F, 548 2–5 Cases were identified among individuals who had immigrated from various places, with the screening process involving history-taking and the collection of significant information. DSM‑5 The prevalence of autism was 3.66% among children aged 2 to 5 years, with higher rates reported among the immigrant population. Collaboration with healthcare personnel could help reduce incidences.
 Taylor et al. [45] 2013 UK Survey study T, 256,278; M, 132,143; F, 124,135 2–8 Cases were identified through media and healthcare records officially maintained by hospitals. DSM‑IV The rate of autism gradually increased to 3.8 per 1,000 boys and 0.8 per 1,000 girls, with a fivefold increase over time.
 Williams et al. [46] 2008 UK Cohort study T, 14,062; M, 7,111; F, 6,951 11 Cases were identified from the Pupil Level Annual Schools Census, with suspected cases diagnosed by healthcare personnel using standardized scales. DSM‑IV Autism is often associated with other chromosomal disorders. Most children with ASD were reported to have neurodevelopmental disorders, including learning and cognitive impairments.
 Scattoni et al. [47] 2023 Italy Survey study T, 35,823 7–9 Samples were identified in 2 phases: in the first phase, data were obtained from local Ministry of Education disability registries; in the second phase, direct screening was conducted in schools. Scores above 15 were considered positive. SCQ-L The study revealed that 13.4% of children were diagnosed with ASD. Most diagnoses occurred at ages 7 to 9, with boys being diagnosed 4.4 times more often than girls. These findings guide health policymakers in implementing appropriate interventions.
Australia
 May et al. [84] 2020 Australia Cohort study T, 3,381; M, 1,690; F, 1,691 12–13 Samples were identified through parents and teachers. Two cohorts were included: “Kinder” and “Birth.” Data were compared between these 2 groups, with and without cohort overlap. SDQ The study revealed that 4.36% of children aged 12–13 years were reported to have ASD. The Kinder cohort exhibited higher social problems and a lower quality of life compared to the Birth cohort, as reported by teachers and parents.
 Bowden et al. [85] 2020 Australia Cohort study T, 1,551,342 0–24 The study identified samples from health records to systematically assess and compare normal children with those diagnosed with autism. DSM‑IV The study findings contribute to the development of screening and diagnostic criteria for autism. They also support the formulation of treatment and rehabilitation policies.
 Randall et al. [86] 2016 Australia Longitudinal study T, 8,366; M, 4,216; F, 4,150 6–7 Children were recruited from kindergarten, and their behaviors, including verbal and nonverbal communication, were observed over a 2-year period. DSM-5 crit The study revealed that children with ASD experienced a lower quality of life and disturbed emotional bonds with their parents and siblings. Approximately 6%–9% of children with mild symptoms were able to behave normally.

T, total; M, male; F, female; CHAT, modified checklist for autism in toddlers; ASD, autism spectrum disorder; ISAA, Indian scale for assessment of autism; SCDC, social and communication disorders checklist; M-CHAT, modified CHAT; ADOS, autism diagnostic observation schedule; SCQ, social communication questionnaire; ASSQ, autism spectrum screening questionnaire; DSM-IV, Diagnostic and Statistical Manual of Mental Disorders; ADI‑R, autism diagnostic interview-revised; CAST, childhood autism spectrum test; CARS, childhood autism rating scale; QSS, Qatar School survey; ADDM, autism and developmental disabilities monitoring; LASI, longitudinal ageing study in India; Q‑CHA, quantitative checklist for autism; ICD, International Classification of Diseases; DAWBA, development and well-being assessment; DISCO, diagnostic interview for social and communication disorders; FSIQ, full-scale IQ; ASDEU, ASD in the European Union; SCQ-L, SCQ-life version; SDQ, strengths and difficulties questionnaire.

Table 2.

Quality appraisal of the included studies using the modified Newcastle-Ottawa scale

Study Published year Country Research design More than 70% representativeness Sample size of more than 250 More than 70% response rate Appropriate tool with cut-off scores Detailed results not requiring further calculations Total score Study quality
Akhter et al. [50] 2018 Bangladesh Cross-sectional * * * - * 4/5 Low risk
Heys et al. [48] 2018 Nepal Cross-sectional - * * - * 3/5 Low risk
Raina et al. [49] 2017 India Cross-sectional - * * * * 4/5 Low risk
Rudra et al. [51] 2017 India Cross-sectional * * - * * 4/5 Low risk
Chaaya et al. [52] 2016 Lebanon Cross-sectional - * * - * 3/5 Low risk
Huang et al. [53] 2014 China Cross-sectional * * * * * 5/5 Low risk
Raz et al. [89] 2015 Israel Survey study * * * * * 5/5 Low risk
Poovathinal et al. [63] 2016 India Community survey * * * - * 4/5 Low risk
Raina et al. [55] 2015 India Cross-sectional * * * - * 4/5 Low risk
Davidovitch et al. [56] 2013 Israel Cross-sectional study * * * * * 5/5 Low risk
Chien et al. [57] 2011 Taiwan Survey study * * * * * 5/5 Low risk
Kim et al. [58] 2011 China Korea Longitudinal study * * * * * 5/5 Low risk
Perera et al. [59] 2009 Sri Lanka Cross-sectional * * * * - 4/5 Low risk
Sun et al. [60] 2015 China Survey study * * * * - 4/5 Low risk
Al-Farsi et al. [87] 2011 Oman Cross-sectional * * * * * 5/5 Low risk
Li et al. [64] 2011 China Survey study * * * * * 5/5 Low risk
Al-Mamri et al. [65] 2019 Oman Retrospective study * * * * * 5/5 Low risk
Alshaban et al. [66] 2019 Qatar Survey study * * * * * 5/5 Low risk
Zhou et al. [67] 2020 China Survey study * * * * * 5/5 Low risk
Sun et al. [88] 2019 China Survey study * * * * * 5/5 Low risk
Jin et al. [61] 2018 China Survey study * * * * * 5/5 Low risk
Al-Zahrani [62] 2013 USA Cross-sectional * * * * * 5/5 Low risk
Nicholas et al. [69] 2009 USA Cohort study * * * * * 5/5 Low risk
Kogan et al. [70] 2018 USA Survey study * * * * * 5/5 Low risk
Baio et al. [71] 2018 USA Survey study * * * * * 5/5 Low risk
Christensen et al. [79] 2016 USA Survey study * * * * * 5/5 Low risk
Durkin et al. [73] 2017 USA Cross-sectional * * * * * 5/5 Low risk
Fombonne et al. [74] 2016 Mexico Survey study * * * * - 4/5 Low risk
Nicholas et al. [75] 2008 USA Survey study - * * * * 4/5 Low risk
Diallo et al. [76] 2018 USA Survey study * * * * - 4/5 Low risk
Dekkers et al. [77] 2015 Ecuador Survey study * * * * * 5/5 Low risk
Montiel-Nava and Pena [78] 2008 Venezuela Cross-sectional * * * * * 5/5 Low risk
Christensen et al. [72] 2019 USA Survey study * * * * * 5/5 Low risk
Shaw et al. [81] 2023 USA Survey study * * * * * 5/5 Low risk
Maenner et al. [90] 2020 USA Survey study * * * * * 5/5 Low risk
Lagunju et al. [68] 2014 Nigeria Cohort study * * * * * 5/5 Low risk
Zeglam and Maound [82] 2012 Libya Cross-sectional * * * * - 4/5 Low risk
Hewitt et al. [83] 2016 Somalia Cross-sectional * * * * * 5/5 Low risk
Kocovska et al. [24] 2012 Faroe Islands Longitudinal study * * * * * 5/5 Low risk
Nygren et al. [25] 2012 Sweden Survey study * * * * * 5/5 Low risk
Morales-Hidalgo et al. [26] 2018 Spain Survey study * * * * * 455 Low risk
Fernell and Gillberg [27] 2010 Sweden Cohort * * * * - 4/5 Low risk
Skonieczna-Zydecka et al. [28] 2017 Poland Survey study * * * * * 5/5 Low risk
Idring et al. [29] 2015 Sweden Cohort * * * * * 5/5 Low risk
Saemundsen et al. [30] 2013 Iceland Cohort * * * * * 5/5 Low risk
Posserud et al. [31] 2010 Norway Survey study * * * * * 5/5 Low risk
Isaksen et al. [32] 2012 Norway Survey study * * * * * 5/5 Low risk
Mattila et al. [33] 2011 Finland Survey study * * * * * 5/5 Low risk
van Bakel et al. [34] 2015 France Survey study * * * * * 5/5 Low risk
Narzisi et al. [12] 2018 Italy Survey study * * * * * 5/5 Low risk
Bachmann et al. [35] 2018 Germany Survey study * * * * - 4/5 Low risk
Baron-Cohen et al. [36] 2009 UK Survey study * * * * - 4/5 Low risk
Hansen et al. [37] 2015 Denmark Survey study - * * * * 4/5 Low risk
Parner et al. [38] 2008 Denmark Cohort study - * * * * 4/5 Low risk
Thomaidis et al. [39] 2020 Greece Cohort study * * * * - 4/5 Low risk
van Balkom et al. [40] 2009 Island Survey study - * * * * 4/5 Low risk
Suren et al. [41] 2012 Norway Survey study * * * * - 4/5 Low risk
Fuentes et al. [42] 2021 Spain Survey study * * * * - 4/5 Low risk
Boilson et al. [43] 2016 Ireland Survey study * * * * * 5/5 Low risk
Linnsand et al. [44] 2021 Sweden Survey study - * * * * 5/5 Low risk
Taylor et al. [45] 2013 UK Survey study * * * * * 4/5 Low risk
Williams et al. [46] 2008 UK Cohort study * * * * * 5/5 Low risk
Scattoni et al. [47] 2023 Italy Survey study * * * * * 5/5 Low risk
May et al. [84] 2020 Australia Cohort study * * * * * 5/5 Low risk
Bowden et al. [85] 2020 Australia Cohort study * * * * * 5/5 Low risk
Randall et al. [86] 2016 Australia Longitudinal study * * * * * 5/5 Low risk
*

, Scores over 3 are considered low-risk; -, zero score.