1.

Individual displays deficient intellectual functioning in areas such as reasoning, problem-solving, planning, abstract thinking, judgment, academic learning, and learning from experience. The deficits are reflected by clinical assessment and intelligence tests.

2.

Individual displays deficient adaptive functioning in at least one area of daily life, such as communication, social involvement, or personal independence, across home, school, work, or community settings. The limitations extend beyond those displayed by most other persons of his or her age and necessitate ongoing support at school, work, or independent living.

3.

The deficits begin during the developmental period (before the age of 18).

(Information from: APA, 2013)