While definitions of intellectual disabilities may provide some insight into the disability itself, it is important that these definitions do not label the person and that generalised assumptions are not made. A person with an intellectual disability may also have a print disability, hearing impairment or physical disability. The onset of this disability occurs before the age of 18. There is a high incidence of epilepsy among people with an intellectual disability. They include an abnormal number of chromosomes, gene defects, maternal infections, Rh incompatibility, head trauma, anoxia, birth injury, early infant infection and, deprived normal development and growth experiences.
Intellectual disability is twice as common in males as in females.
It is estimated that 2.3 percent of the Australian population have some level of intellectual disability. In the state of Victoria it is believed that approximately one percent of the population has some level of intellectual disability, with the Department of Human Services being aware of 60 percent of these people. The inability to process information and effectively communicate with other people is possibly the most notable implication for every day living. As communicating is often taken for granted by most members of society, people with an intellectual disability can struggle to express their needs. A deficit in intellectual functioning and associated disabilities can have a significant effect on an individual's education, leisure, employment and social and personal opportunities.