Challenging Your Intellect ---- What do you know about Intellectual Disability?

Some time ago, a wrong arrest made by the police aroused great public attention. Although the police were dutifully arresting a suspect, the public found their method of interrogation very questionable. Using leading questions in interrogation is prohibited, as it could lead to charges in innocent people, not to mention that the arrested person was an individual suffering from moderate intellectual disability (ID) and autism. Using leading questions on such mentally incapacitated individuals could cause them to wrongly admit charges. So what behaviours do individuals with ID display that help us differentiate them from people without it? What capabilities do these individuals have? And what do we need to take note of should we need to communicate with these individuals?


According to the Diagnostic and Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM 5), the 'bible' of psychiatry, ID is a kind of neurodevelopmental disorder. To diagnose a person with the disability, the person has to meet the following criteria:

  1. Deficits in intellectual functioning: intellectual functioning includes abilities such as problem-solving, reasoning, planning, judgment, and abstract thinking. These abilities in individuals with intellectual disability would be substantially below average when compared to people of their age (IQ 70 or below).
  2. Deficits in adaptive functioning: adaptive functioning refers to the ability to solve daily-life problems in the conceptual domain (including skills in reading and writing, math, and understanding and expressing language), social domain (including interpersonal communication skills, the ability to make and retain friendships), and practical domain (such as personal care, money management, use of public facilities, work-related skills).
  3. These limitations occur during the developmental period (i.e. during childhood or adolescence).

The severity of ID is diagnosed based on the level of impairment in adaptive functioning, which place individuals with the disability in 4 main categories: mild, moderate, severe, and profound.

If you have been reading the criteria carefully, you may notice that having odd facial features is NOT one of the diagnostic criteria. Some of the individuals with ID do have distinguishable facial features, such as those with Down’s Syndrome have upward-slanting eyes, flat noses, and larger and protruding tongues. In fact most individuals with ID look indistinguishable from typically-developing people (except those with severe and profound intellectual disability). The only difference is their significant difference in intellectual and adaptive abilities.


So what levels of abilities do people with varying severities of ID have? Below is a description by the 10th version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10), which is a medical classification list by the World Health Organization (WHO):

  1. Mild ID: Adults’ mental age ranges from 9 to under 12 years. They can acquire basic self-care skills (e.g. spontaneously wash-up, use public transport), but would likely have some learning difficulties in learning academic knowledge and expressing themselves. Vocational skills would also be weak. But many will be able to work and maintain good social relationships and contribute to society.
  2. Moderate ID: Adults’ mental age ranges from 6 to under 9 years. They would have very weak self-care abilities, and would require adult supervision and assistance. They can be capable of basic academic skills (e.g. basic arithmetic like addition and subtraction), but due to their significantly sub-average abilities they would not be suitable for mainstream schooling. Adults may be able to work under supervision in sheltered workshops, but their quality and productivity would be low, and will need varying degrees of support to live and work in the community.
  3. Severe ID: Adults’ mental age ranges from 3 to under 6 years. Self-care and academic learning skills are severely lacking, and they have very limited ability to communicate (e.g. single words). They would have continuous need for support in life.
  4. Profound ID: Adults have mental age of below 3 years. This results in severe limitation in self-care, continence, communication and mobility, and would require continuous support in life.


Based on the above descriptive, it is likely that the innocent ‘suspect’ was not able to comprehend the complex questions in the interrogation, and his responses were probably guesses or simply parroting the speech of policemen, and thus cannot be regarded as valid testimony. So what are some of the strategies to communicate more effectively with people with ID? Due to their limited capability in comprehending language, simple language should be used when giving them instructions or asking questions. Using communication aid (e.g. picture exchange communication system) can also help facilitate their communication. The more severe the disability is, the simpler the language you have to use for that individual.


Although their capabilities are limited, like any human being they also yearn to be accepted and treated nicely by people, and make friends with others. If you are able to understand and accept their limitations and build relationships with them based on their capabilities, you may discover the friendly sides of them!



American Psychiatric Association., & American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders: DSM-5. Washington, D.C: American Psychiatric Association.


Hong Chi Association (2007). 親子溝通樂系列. Hong Kong: Hong Chi Association.


World Health Organization. (2010). International Statistical Classification of Diseases and Related Health Problems (10th revision). Retrieved from