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The epidemiology of autism is the study of factors affecting autism spectrum disorders (ASD). A 2012 review of global prevalence estimates of autism spectrum disorders found a median of 62 cases per 10,000 people. There is a lack of evidence from low- and middle-income countries though.〔 ASD averages a 4.3:1 male-to-female ratio.〔 The number of children known to have autism 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.〔 The risk of autism is associated with several prenatal factors, including advanced parental age and diabetes in the mother during pregnancy.〔 ASD is associated with several genetic disorders〔 and with epilepsy.〔 Autism is a complex neurodevelopmental disorder. Many causes have been proposed, but its theory of causation is still questionable and ultimately unknown. Autism is believed to be largely inherited, although the genetics of autism are complex and it is unclear which genes are responsible. Little evidence exists to support associations with specific environmental exposures.〔 In rare cases, autism is strongly associated with agents that cause birth defects. Other proposed causes, such as childhood vaccines, are controversial and the vaccine hypotheses lack convincing scientific evidence.〔 Andrew Wakefield, the doctor whose study linked Autism with childhood vaccines, has since had his licence revoked in the United Kingdom for medical fraud.〔''Wakefield's article linking MMR vaccine and autism was fraudulent''. BMJ. 2011. 342:c7452. Retrieved April 2, 2012. http://www.bmj.com/content/342/bmj.c7452〕〔A J Wakefield, S H Murch, A Anthony, J Linnell, et al. ''Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children''. Vol 351. The Lancet. February 28, 1998. http://briandeer.com/mmr/lancet-paper.pdf〕 ==Frequency== Although incidence rates measure autism risk directly, most epidemiological studies report other frequency measures, typically point or period prevalence, or sometimes cumulative incidence. Attention is focused mostly on whether prevalence is increasing with time.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Epidemiology of autism」の詳細全文を読む スポンサード リンク
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