Two professional associations have each developed their own diagnostic criteria for intellectual disabilities (ID). Each has its own merits:
1. The American Psychiatric Association (APA), which publishes the Diagnostic and Statistical Manual of Mental Disorders (DSM-5, APA 2013);
2. The American Association on Intellectual and Developmental Disabilities (AAIDD formerly AAMR).
Let's review these two systems in greater detail.
The American Psychiatric Association (APA) diagnostic criteria for intellectual disability (DSM-5 criteria)
The American Psychiatric Association's (APA) diagnostic criteria for intellectual disability (ID, formerly mental retardation) are found in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5, APA 2013). A summary of the diagnostic criteria in DSM-5 are as follows:
1. Deficits in intellectual functioning
This includes various mental abilities:
- Problem solving;
- Abstract thinking;
- Academic learning (ability to learn in school via traditional teaching methods);
- Experiential learning (the ability to learn through experience, trial and error, and observation).
These mental abilities are measured by IQ tests. A score of approximately two standard deviations below average represents a significant cognitive deficit. These scores would occur about 2.5% of the population. Or stated differently, 97.5% of people of the same age and culture would score higher. The tests used to measure IQ must be standardized and culturally appropriate. This is typically an IQ score of 70 or below.
2. Deficits or impairments in adaptive functioning
This includes skills needed to live in an independent and responsible manner. Limited abilities in these life skills make it difficult to achieve age appropriate standards of behavior. Without these skills, a person needs additional supports to succeed at school, work, or independent life. Deficits in adaptive functioning are measured using standardized, culturally appropriate tests.
Various skills are needed for daily living:
- Communication: This refers to the ability to convey information from one person to another. Communication is conveyed through words and actions. It involves the ability to understand others, and to express one's self through words or actions.
- Social skills: This refers to the ability to interact effectively with others. We usually take social skills for granted. However, these skills are critical for success in life. These skills include the ability to understand and comply with social rules, customs, and standards of public behavior. This intricate function requires the ability to process figurative language and detect unspoken cues such as body language.
- Personal independence at home or in community settings: This refers to the ability to take care of yourself. Some examples are bathing, dressing, and feeding. It also includes the ability to safely complete day-to-day tasks without guidance. Some examples are cooking, cleaning, and laundry. There are also routine activities performed in the community. This includes shopping for groceries, and accessing public transportation.
- School or work functioning: This refers to the ability to conform to the social standards at work or school. It includes the ability to learn new knowledge, skills, and abilities. Furthermore, people must apply this information in a practical, adaptive manner; without excessive direction or guidance.
3. These limitations occur during the developmental period. This means problems with intellectual or adaptive functioning were evident during childhood or adolescence. If these problems began after this developmental period, the correct diagnosis would be neurocognitive disorder. For instance, a traumatic brain injury from a car accident could cause similar symptoms.