The<unk>  is the study of the incidence and distribution of<unk>  spectrum disorders (ASD). A 2012 review of global prevalence estimates of<unk>  spectrum disorders found a median of 62 cases per 10,000 people. In contrast, a 2016 review of global prevalence estimates of<unk>  spectrum disorders found a median of 18.5 cases per 10,000 people. However there is a lack of evidence from low- and middle-income countries. ASD averages a 4.3:1 male-to-female ratio in diagnosis, not accounting for ASD in gender diverse populations, which overlap disproportionately with ASD populations. The number of children known to have<unk>  has increased dramatically since the 1980s, at least partly due to changes in diagnostic practice; it is unclear whether prevalence has actually increased; and as-yet-unidentified environmental risk factors cannot be ruled out. In 2020, the Centers for Disease Control’s<unk>  and Developmental Disabilities Monitoring (ADDM) Network reported that approximately 1 in 54 children in the United States (1 in 34 boys, and 1 in 144 girls) is diagnosed with an<unk>  spectrum disorder (ASD), based on data collected in 2016. This estimate is a 10% increase from the 1 in 59 rate in 2014, 105% increase from the 1 in 110 rate in 2006 and 176% increase from the 1 in 150 rate in 2000. Diagnostic criteria of ASD has changed significantly since the 1980s; for example, U.S. special-education<unk>  classification was introduced in 1994. ASD is a complex neurodevelopmental disorder, and although what causes it is still not entirely known, efforts have been made to outline causative mechanisms and how they give rise to the disorder. The risk of developing<unk>  is increased in the presence of various prenatal factors, including advanced paternal age and diabetes in the mother during pregnancy. In rare cases,<unk>  is strongly associated with agents that cause birth defects. It has been shown to be related to genetic disorders and with epilepsy. ASD is believed to be largely inherited, although the genetics of ASD are complex and it is unclear which genes are responsible. ASD is also associated with several intellectual or emotional gifts, which has led to a variety of hypotheses from within evolutionary psychiatry that<unk> ic traits have played a beneficial role over human evolutionary history. Other proposed causes, such as childhood vaccines, are controversial. The vaccine hypothesis has been extensively investigated and shown to be false, lacking any scientific evidence. Andrew Wakefield published a small study in 1998 in the United Kingdom suggesting a causal link between<unk>  and the trivalent MMR vaccine. After data included in the report was shown to be deliberately falsified, the paper was retracted, and Wakefield was struck off the medical register in the United Kingdom. It is problematic to compare<unk>  rates over the last three decades, as the diagnostic criteria for<unk>  have changed with each revision of the Diagnostic and Statistical Manual (DSM), which outlines which symptoms meet the criteria for an ASD diagnosis. In 1983, the DSM did not recognize PDD-NOS or Asperger’s syndrome, and the criteria for<unk> ic disorder (AD) were more restrictive. The previous edition of the DSM, DSM-IV, included<unk> ic disorder, childhood disintegrative disorder, PDD-NOS, and Asperger’s syndrome. Due to inconsistencies in diagnosis and how much is still being learnt about<unk> , the most recent DSM (DSM-5) only has one diagnosis,<unk>  spectrum disorder (ASD), which encompasses each of the previous four disorders. According to the new diagnostic criteria for ASD, one must have both struggles in social communication and interaction and restricted repetitive behaviors, interests and activities (RRBs). ASD diagnoses continue to be over four times more common among boys (1 in 34) than among girls (1 in 154), and they are reported in all racial, ethnic and socioeconomic groups. Studies have been conducted in several continents (Asia, Europe and North America) that report a prevalence rate of approximately 1 to 2 percent. A 2011 study reported a 2.6 percent prevalence of<unk>  in South Korea.
Epidemiology of autism
Genetics of post-traumatic stress disorder
Epidemiology of attention deficit hyperactive disorder
Epidemiology of schizophrenia
Prognosis of schizophrenia
Mechanism of autism
Epidemiology of child psychiatric disorders
Psychiatric genetics