4433.0.55.003 - Intellectual Disability, Australia, 2012  
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In 2012 there were around 668,100 Australians (2.9%) with intellectual disability, which represents a statistically significant increase from the estimated 565,000 people (2.6%) with intellectual disability in the 2009 SDAC.

In 2012, intellectual disability was most common in the very young and very old, with prevalence rates of 4% for children aged 0-14 years and 10% for people aged 75 years and over. Children made up the largest proportion of the population with intellectual disability, with around one-quarter being under the age of 15 years.

Overall, the rates of intellectual disability were higher for men (3.3%) than for women (2.6%). As shown in Graph 1, this was true in every age group except for those aged 75 years and older, where women had a higher rate than men. The difference was particularly marked for boys aged 0-14 years who were twice as likely to have intellectual disability than girls in the same age group. A similar pattern is seen in the data from the 2009 SDAC. This is possibly due to the fact that boys have higher rates of some conditions that are more commonly associated with intellectual disability. For example, young boys in this age group were 3.6 times more likely to have Autism or a related disorder than girls (50,500 boys compared with 13,900 girls). Other possible reasons for a higher prevalence in boys include more frequent identification among boys due to abnormal behavioural patterns in school, and increased adverse effect of maternal smoking and low birth-weight on neurological development among males (Endnote 2).

Graph 1: Prevalence of Intellectual Disability, by age groups and sex, 2012

The higher rates of intellectual disability among older women aged 75 years and over (11%) compared with older men (8%) may be due to the fact that women are more likely than men to have ageing associated diseases which impact on cognitive functioning. In 2012, rates of dementia were higher for women over 75 years (9%) compared with men of the same age (6%).