text: The epidemiology of<unk>  is the study of factors affecting<unk>  spectrum disorders (ASD). Most recent reviews estimate a prevalence of one to two cases per 1,000 people for<unk> , and about six per 1,000 for ASD; because of inadequate data, these numbers may underestimate ASD's true prevalence. ASD averages a 4.3:1 male-to-female ratio. The number of children known to have<unk>  has increased dramatically since the 1980s, at least partly due to changes in diagnostic practice; the question of whether actual prevalence has increased is unresolved, and as-yet-unidentified contributing environmental risk factors cannot be ruled out. The risk of<unk>  is associated with several prenatal and perinatal factors, including advanced parental age and low birth weight. ASD is associated with several genetic disorders and with epilepsy, and<unk>  is associated with mental retardation.
option_0: Autism epidemiology
option_1: Mental retardation epidemiology and demographics
option_2: Hearing impairment epidemiology and demographics
option_3: Dementia epidemiology and demographics
option_4: Deafness epidemiology and demographics
option_5: Attention-deficit hyperactivity disorder classification
option_6: Schizophrenia epidemiology and demographics
option_7: Attention-deficit hyperactivity disorder epidemiology and demographics