Intellectual disability

The Wechsler Intelligence Scales (such as the WAIS for adults or WISC for children) are standardized tools used to assess intellectual functioning. Scores on these scales are represented as Full-Scale IQ (FSIQ) scores, which follow a bell curve distribution. Here's a breakdown of the scoring and how it relates to intellectual functioning:

Wechsler IQ Score Ranges

1. Average Range: IQ scores from 90–109 (50th percentile) are considered average, representing the majority of the population.

2. Below Average Range:

   • Low Average: IQ scores from 80–89 (about the 9th–24th percentile).

   • Borderline: IQ scores from 70–79 (about the 2nd–8th percentile).

3. Extremely Low: IQ scores below 70 (below the 2nd percentile) often indicate significant cognitive challenges.

Percentile Interpretation

• The 1st percentile means that only about 1% of individuals in the normative sample score at or below this level.

• This corresponds roughly to an IQ of 65, depending on the test's standardization.

Intellectual Disabilities and Wechsler Scores

Intellectual disability (ID) is characterized by significant limitations in intellectual functioning (IQ) and adaptive functioning, and it must onset during the developmental period. Below are general guidelines for the relationship between Wechsler IQ scores and classifications of ID:

1. Mild Intellectual Disability

   • IQ Range: 50–70

   • Percentile: ~2nd percentile or below

   • Description: Individuals often learn academic skills up to a 6th-grade level. With support, they can achieve independence in many areas, such as employment and daily living.

2. Moderate Intellectual Disability

   • IQ Range: 35–49

   • Percentile: Below the 1st percentile

   • Description: These individuals typically achieve academic skills equivalent to 2nd-grade levels. They can perform simple tasks with supervision and support and may require more structured environments for work and daily living.

3. Severe Intellectual Disability

   • IQ Range: 20–34

   • Percentile: Far below the 1st percentile

   • Description: Individuals have very limited communication and academic abilities. They rely on intensive support for all aspects of daily living, including personal care.

4. Profound Intellectual Disability

   • IQ Range: Below 20

   • Percentile: Extremely rare and not typically represented on standardized scales

   • Description: These individuals require round-the-clock care and have minimal communication and self-care abilities