the 200–2004 school year found a prevalence rate of 0.68% (or 1 per 147). a 2001 review of the medical research conducted by the public health agency of canada concluded that there was no link between mmr vaccine and either inflammatory bowel disease or autism. the review noted, "an increase in cases of autism was noted by year of birth from 1979 to 1992; however, no incremental increase in cases was observed after the introduction of mmr vaccination." after the introduction of mmr, "a time trend analysis found no correlation between prevalence of mmr vaccination and the incidence of autism in each birth cohort from 1988 to 1993." united states cdc's most recent estimate is that 1 out of every 44 children, or 23 per 1,000, have some form of asd as of 2018. the number of diagnosed cases of autism grew dramatically in the u.s. in the 1990s and have continued in the 2000s. for the 2006 surveillance year, identified asd cases were an estimated 9.0 per 1000 children aged 8 years (95% confidence interval = 8.6–9.3). these numbers measure what is sometimes called "administrative prevalence", that is, the number of known cases per unit of population, as opposed to the true number of cases. this prevalence estimate rose 57% (95% ci 27%–95%) from 2002 to 2006. the national health interview survey (nhis) for 2014–2016 studied 30,502 us children and adolescents and found the weighted prevalence of asd was 2.47% (24.7 per 1,000); 3.63% in boys and 1.25% in girls. across the 3-year reporting period, the prevalence was 2.24% in 2014, 2.41% in 2015, and 2.76% in 2016. the number of new cases of autism spectrum disorder (asd) in caucasian boys is roughly 50% higher than found in hispanic children, and approximately 30% more likely to occur than in non-hispanic white children in the united states. a further study in 2006 concluded that the apparent rise in administrative prevalence was the result of diagnostic substitution, mostly for findings of intellectual disability and learning disabilities. "many of the children now being counted in the autism category would probably have been counted in the mental retardation or learning disabilities categories if they were being labeled 10 years ago instead of today," said researcher paul shattuck of the waisman center at the university of wisconsin–madison, in a statement. a population-based study in olmsted county, minnesota county found that the cumulative incidence of autism grew eightfold from the 1980–83 period to the 1995–97 period. the increase occurred after the introduction of broader, more-precise diagnostic criteria, increased service availability, and increased awareness of autism. during the same period, the reported number of autism cases grew 22-fold in the same location, suggesting that counts reported by clinics or schools provide misleading estimates of the true incidence of autism. venezuela a 2008 study in venezuela reported a prevalence of 1.1 per 1,000 for autism and 1.7 per 1,000 for asd. asia a journal reports that the median prevalence of asd among 2–6-year-old children who are reported in china from 2000 upwards was 10.3/10,000. hong kong a 2008 hong kong study reported an asd incidence rate similar to those reported in australia and north america, and lower than europeans. it also reported a prevalence of 1.68 per 1,000 for children under 15 years. japan a 2005 study of a part of yokohama with a stable population of about 300,000 reported a cumulative incidence to age 7 years of 48 cases of asd per 10,000 children in 1989, and 86 in 1990. after the vaccination rate of the triple mmr vaccine dropped to near zero and was replaced with mr and m vaccine, the incidence rate grew to 97 and 161 cases per 10,000 children born in 1993 and 1994, respectively, indicating that the combined mmr vaccine did not cause autism. a 2004 japanese autism association reported that about 360.000 people have typical kanner-type autism. israel a 2009 study reported that the annual incidence rate of israeli children with a diagnosis of asd receiving disability benefits rose from zero in 1982–1984 to 190 per million in 2004. it was not known whether these figures reflected true increases or other factors such as changes in diagnostic measures. saudi arabia studies of autism frequency have been particularly rare in the middle east. one rough estimate is that the prevalence of autism in saudi arabia is 18 per 10,000, slightly higher than the 13 per 10,000 reported in developed countries.(compared to 168 per 10,000 in the usa) denmark in 1992, thiomersal-containing vaccines were removed in denmark. a study at aarhus university indicated that during the chemical's usage period (up through 1990), there was no trend toward an increase in the incidence of autism. between 1991 and 2000 the incidence increased, including among children born after the discontinuation of thimerosal. france france made autism the national focus for the year 2012 and the health ministry estimated the rate of autism in 2012 to have been 0.67%, i.e. 1 in 150. eric fombonne made some studies in the years 1992 and 1997. he found a prevalence of 16 per 10,000 for the global pervasive developmental disorder (pdd). the inserm found a prevalence of 27 per 10,000 for the asd and a prevalence of 9 per 10,000 for the early infantile autism in 2003. those figures are considered as underrated as the who gives figures between 30 and 60 per 10,000. the french minister of health gives a prevalence of 4.9 per 10,000 on its website but it counts only early infantile autism. germany a 2008 study in germany found that inpatient admission rates for children with asd increased 30% from 2000 to 2005, with the largest rise between 2000 and 2001 and a decline between 2001 and 2003. inpatient rates for all mental disorders also rose for ages up to 15 years, so that the ratio of asd to all admissions rose from 1.3% to 1.4%. norway a 2009 study in norway reported prevalence rates for asd ranging from 0.21% to 0.87%, depending on assessment method and assumptions about non-response, suggesting that methodological factors explain large variances in prevalence rates in different studies. united kingdom the incidence and changes in incidence with time are unclear in the united kingdom. the reported autism incidence in the uk rose starting before the first introduction of the mmr vaccine in 1989. however, a perceived link between the two arising from the results of a fraudulent scientific study has caused considerable controversy, despite being subsequently disproved. a 2004 study found that the reported incidence of pervasive developmental disorders in a general practice research database in england and wales grew steadily during 1988–2001 from 0.11 to 2.98 per 10,000 person-years, and concluded that much of this increase may be due to changes in diagnostic practice. genetics further information: heritability of autism as late as the mid-1970s there was little evidence of a genetic role in autism; evidence from genetic epidemiology studies now suggests that it is one of the most heritable of all psychiatric conditions. the first studies of twins estimated heritability to be more than 90%; in other words, that genetics explains more than 90% of autism cases. when only one identical twin is autistic, the other often has learning or social disabilities. for adult siblings, the risk of having one or more features of the broader autism phenotype might be as high as 30%, much higher than the risk in controls. about 10–15% of autism cases have an identifiable mendelian (single-gene) condition, chromosome abnormality, or other genetic syndrome, and asd is associated with several genetic disorders. since heritability is less than 100% and symptoms vary markedly among identical twins with autism, environmental factors are most likely a significant cause as well. if some of the risk is due to gene-environment interaction the 90% heritability may be too high; however, in 2017, the largest study, including over three million participants, estimated the heritability at 83%. genetic linkage analysis has been inconclusive; many association analyses have had inadequate power. studies have examined more than 100 candidate genes; many genes must be examined because more than a third of genes are expressed in the brain and there are few clues on which are relevant to autism. causative factors main article: causes of autism a few studies have found an association between autism and frequent use of acetaminophen (e.g. tylenol, paracetamol) by the mother during pregnancy. autism is also associated with several other prenatal factors, including advanced age in either parent, and diabetes, bleeding, or use of psychiatric drugs in the mother during pregnancy. autism was found to be indirectly linked to prepregnancy obesity and low weight mothers. it is not known whether mutations that arise spontaneously in autism and other neuropsychiatric disorders come mainly from the mother or the father, or whether the mutations are associated with parental age. however, recent studies have identified advancing paternal age as a significant indicator for asd. increased chance of autism has also been linked to rapid "catch-up" growth for children born to mothers who had unhealthy weight at conception. a large 2008 population study of swedish parents of children with autism found that the parents were more likely to have been hospitalized for a mental disorder, that schizophrenia was more common among the mothers and fathers, and that depression and personality disorders were more common among the mothers. it is not known how many siblings of autistic individuals are themselves autistic. several studies based on clinical samples have given quite different estimates, and these clinical samples differ in important ways from samples taken from the general community. autism has also been shown to cluster in urban neighborhoods of high socioeconomic status. one study from california found a three to fourfold increased risk of autism in a small 30 by 40 km region centered on west hollywood, los angeles. gender differences share of males vs. females with autistic spectrum disorder, owid boys have a higher chance of being diagnosed with autism than girls. the asd sex ratio averages 4.3:1 and is greatly modified by cognitive impairment: it may be close to 2:1 with intellectual disability and more than 5.5:1 without. recent studies have found no association with socioeconomic status, and have reported inconsistent results about associations with race or ethnicity. rora deficiency may explain some of the difference in frequency between males and females. rora protein levels are higher in the brains of typically developing females compared to typically developing males, providing females with a buffer against rora deficiency. this is known as the female protective effect. rora deficiency has previously been proposed as one factor that may make males more vulnerable to autism. there is a statistically notable overlap between asd populations and gender diverse populations. comorbid conditions further information: conditions comorbid to autism spectrum disorders autism is associated with several other conditions: genetic disorders. about 10–15% of autism cases have an identifiable mendelian (single-gene) condition, chromosome abnormality, or other genetic syndrome, and asd is associated with several genetic disorders. intellectual disability. the fraction of autistic individuals who also meet criteria for intellectual disability has been reported as anywhere from 25% to 70%, a wide variation illustrating the difficulty of assessing autistic intelligence. anxiety disorders are common among children with asd, although there are no firm data. symptoms include generalized anxiety and separation anxiety, and are likely affected by age, level of cognitive functioning, degree of social impairment, and asd-specific difficulties. many anxiety disorders, such as social phobia, are not commonly diagnosed in people with asd because such symptoms are better explained by asd itself, and it is often difficult to tell whether symptoms such as compulsive checking are part of asd or a co-occurring anxiety problem. the prevalence of anxiety disorders in children with asd has been reported to be anywhere between 11% and 84%. epilepsy, with variations in risk of epilepsy due to age, cognitive level, and type of language disorder; 5–38% of children with autism have comorbid epilepsy, and only 16% of these have remission in adulthood. several metabolic defects, such as phenylketonuria, are associated with autistic symptoms. minor physical anomalies are significantly increased in the autistic population. preempted diagnoses. although the dsm-iv rules out concurrent diagnosis of many other conditions along with autism, the full criteria for adhd, tourette syndrome, and other of these conditions are