People with an intellectual disability are considered to have a diminished capacity for reasoning, planning, problem solving, abstract thinking, comprehending complex ideas, learning efficiently, and learning from experience -- as determined by a standardized test of intelligence, most often an IQ test. An individual intellectual disability diagnosis falls on a spectrum from mild to moderate to severe to profound. Those considered to have a moderate intellectual disability “can take care of themselves, travel to familiar places in their community, and learn basic skills related to safety and health.” Their self-care requires moderate support. Severe intellectual disabilities result in major delays in development. Students with this diagnosis often have the ability to understand speech, but have limited communication skills. Though these students may be able to learn simple daily routines and to engage in simple self-care, individuals with a severe diagnosis will need supervision in social settings and will likely be unable to live independently as adults.
In a survey covering the years 1997 to 2008, the prevalence of ID was .78 percent among boys and .63 percent among girls. Among the total cases of ID, 85 percent fall under the mild diagnosis, 10 percent are moderate, 3.5 percent are severe, and 1.5 percent are considered profound.
(Boat & Wu 2015)