| Prevalence |
Approximately 1% of the general population has intellectual disability; however, prevalence estimates vary depending on the age, the survey method used, and the particular population studied. |
| Onset |
Severe and profound intellectual disability are generally identified at birth, although in some cases intellectual disability is caused by a medical condition later in childhood, such as head trauma. Mild intellectual disability is sometimes not diagnosed until relatively late in childhood, although the onset may have been earlier. |
| Comorbidity |
Compared to the general population, people with intellectual disability are three to four times more likely to have an additional psychological disorder, cerebral palsy, or epilepsy. Among the most common comorbid disorders are major depressive disorder, attention-deficit/hyperactivity disorder, and autism spectrum disorder. |
| Course |
The diagnosis is typically lifelong for moderate to severe intellectual disability, but beneficial environmental factors can improve adaptive functioning for those with mild intellectual disability to the point where they no longer meet all the criteria for the disorder. Educational opportunities, support, and stimulation can improve the level of functioning. |
| Gender Differences |
Intellectual disability occurs more frequently in males, with a male-to-female ratio of about 1.5 to 1. |
| Cultural Differences |
Although the criteria for intellectual disability used in many other countries are similar to those used in the United States, they are not always the same; such differences may account for the higher prevalence rates in some other countries, such as 4.5% in France (Oakland et al., 2003). |
| Source: Unless otherwise noted, the source for information is American Psychiatric Association, 2013. |