Mental retardation (MR) is a condition diagnosed before age 18, usually in infancy or prior to birth, that includes below-average general intellectual function, and a lack of the skills necessary for daily living. When onset occurs at age 18 or after, it is called dementia, which can coexist with an MR diagnosis. Intelligence level as determined by individual standard assessment is below 70, and the ability to adapt to the demands of normal life is impaired. This is important because it distinguishes a diagnosis of MR from individuals with low IQ scores who are able to adapt to the demands of everyday life. Education, job training, support from family, and individual characteristics such as motivation and personality can all contribute to the ability of individuals with MR to adapt.
Other behavioral traits associated with MR (but not deemed criteria for an MR diagnosis) include aggression, dependency, impulsivity, passivity, self-injury, stubbornness, low self-esteem, and low frustration tolerance. Some may also exhibit mood disorders such as psychotic disorders and attention difficulties, though others are pleasant, otherwise healthy individuals. Sometimes physical traits, like shortness in stature and malformation of facial elements, can set individuals with MR apart, while others may have a normal appearance.