Mild, Moderate, Severe Intellectual Disability Differences

Experts divide the types of cognitive impairment into four categories: mild intellectual disability, moderate intellectual disability, severe intellectual disability, and profound intellectual disability. The degree of impairment from an intellectual disability varies widely. DSM-V places less emphasis on the degree of impairment (i.e. IQ scores) and more on the amount and type of intervention needed.

While IQ scores are still relevant and important in assessing the level of intellectual disability, the new DSM-V adds another layer of diagnostic criteria (Intellectual Disability: Causes and Characteristics). Mental health professionals must consider the person's ability or impairment across three skill areas: conceptual, social, and practical life skill.

The category details are as follows:

Mild intellectual disability

• IQ 50 to 70
• Slower than typical in all developmental areas
• No unusual physical characteristics
• Able to learn practical life skills
• Attains reading and math skills up to grade levels 3 to 6
• Able to blend in socially
• Functions in daily life

About 85 percent of people with intellectual disabilities fall into the mild category and many even achieve academic success. A person who can read, but has difficulty comprehending what he or she reads represents one example of someone with mild intellectual disability.

Moderate intellectual disability

• IQ 35 to 49
• Noticeable developmental delays (i.e. speech, motor skills)
• May have physical signs of impairment (i.e. thick tongue)
• Can communicate in basic, simple ways
• Able to learn basic health and safety skills
• Can complete self-care activities
• Can travel alone to nearby, familiar places

People with moderate intellectual disability have fair communication skills, but cannot typically communicate on complex levels. They may have difficulty in social situations and problems with social cues and judgment. These people can care for themselves, but might need more instruction and support than the typical person. Many can live in independent situations, but some still need the support of a group home. About 10 percent of those with intellectual disabilities fall into the moderate category.

Severe intellectual disability

• IQ 20 to 34
• Considerable delays in development
• Understands speech, but little ability to communicate
• Able to learn daily routines
• May learn very simple self-care
• Needs direct supervision in social situations

Only about 3 or 4 percent of those diagnosed with intellectual disability fall into the severe category. These people can only communicate on the most basic levels. They cannot perform all self-care activities independently and need daily supervision and support. Most people in this category cannot successfully live an independent life and will need to live in a group home setting.

Profound intellectual disability

• IQ less than 20
• Significant developmental delays in all areas
• Obvious physical and congenital abnormalities
• Requires close supervision
• Requires attendant to help in self-care activities
• May respond to physical and social activities
• Not capable of independent living

People with profound intellectual disability require round-the-clock support and care. They depend on others for all aspects of day-to-day life and have extremely limited communication ability. Frequently, people in this category have other physical limitations as well. About 1 to 2 percent of people with intellectual disabilities fall into this category.

According to the new DSM-V, though, someone with severe social impairment (so severe they would fall into the moderate category, for example) may be placed in the mild category because they have an IQ of 80 or 85. So the changes in the DSM-V require mental health professionals to assess the level of impairment by weighing the IQ score against the person's ability to perform day-to-day life skills and activities. (Read about the types of intellectual disabilities.)

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