IDD Frequently Asked Questions

According to Federal guidelines, I/DD must be present and diagnosed before the person’s 22nd birthday. In practice, unless the I/DD is caused by an injury or illness during childhood, most I/DD’s begin in very early childhood or during gestation, although the symptoms may not be recognized until later. To muddy the water just a little bit, be aware that in North Carolina (but not all States), a person can be considered to have an I/DD if he or she had a traumatic brain injury after the age of 22. (See https://nccdd.org/resources/what-is-i-dd.html).

The current cutoff score on standardized intelligence tests is 70 (for tests that have a mean of 100 and a standard deviation of 15), but the person must also have challenges in 3 or more areas of daily living, usually measured by scores on a social-adaptive assessment. According to Federal guidelines, I/DD must be present and diagnosed before the person’s 22nd birthday. Some of the most commonly used assessments of social-adaptive skills include the Scales of Independent Behavior and the Vineland Adaptive Behavior Scales.

ADHD (Attention Deficit Hyperactivity Disorder) is considered a developmental disability ADHD is not an intellectual disability.

Autism by itself is not an intellectual disability, but approximately 70% of individuals with autism also have an intellectual disability. (e.g., see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4185273/#:~:text=Both%20exist%20together%20in%20the,Wilkins%20and%20Matson%2C%202009).

Dyslexia is a learning disorder, but is not an intellectual disability. For more information, see https://www.mayoclinic.org/diseases-conditions/dyslexia/symptoms-causes/syc-20353552.

Although most people (around 95%) with Down syndrome have intellectual disability, Down syndrome itself is not an intellectual disability. It is still considered a developmental disability, however.

IQ stands for “Intelligence Quotient.” IQ is measured by standardized assessments, such as the Stanford-Binet, Kaufman, or Wechsler instruments. Most measures use 100 as the mean or average score, with standard deviations of 15. Therefore, the cutoff for intellectual disability would typically be 70. Consequently, scores approximately between 50 and 69 would be considered “mild” impairment, scores approximately between 35 and 49 would be considered “moderate” impairment, scores approximately between 20 and 34 would be considered “severe” impairment, and scores lower than 20 would be considered “profound” impairment. 

It’s important to remember that intelligence tests are designed to result in scores that match the normal curve, described above. Therefore, additional information is necessary, usually scores from social-adaptive instruments, in order to make a diagnosis of intellectual disability. The psychologist implementing the assessment also has discretion to interpret the results based on the statistical characteristics of the instruments used, as well as the health and behavior of the individual assessed.  Also, remember that the focus is changing from identifying the level of disability of each person, to identifying the amount and kinds of resources that each person needs in order to function at his or her optimal level.

DD stands for developmental disability.

CP stands for cerebral palsy, which is considered a developmental disability. Cerebral palsy is caused by oxygen deprivation during the birth process and results in physical impairment of the legs, arms, or both, and often affects the person’s physical ability to speak. While about 70% of individuals with CP also have intellectual disability, some people with CP are highly intelligent. More information about CP can be found here: https://www.cdc.gov/ncbddd/cp/facts.html#:~:text=Cerebral%20palsy%20(CP)%20is%20a,problems%20with%20using%20the%20muscles.

FAS stands for fetal alcohol syndrome, a condition caused by the mother’s use of any alcohol during pregnancy. FAS usually results in the child having some level of intellectual impairment, impulsivity, and poor judgment, along with changes in facial features, and sometimes damage to other body systems, such as kidneys or heart. FASD stands for fetal alcohol spectrum disorder and includes the same symptoms as FAS but to a lesser degree or with not all the symptoms present. More information about FAS and FASD can be found here: https://my.clevelandclinic.org/health/diseases/15677-fetal-alcohol-syndrome.

SQ stands for “Social Quotient,” which is similar to IQ or Intelligence Quotient. SQ is a generic way to describe scores achieved on social-adaptive measures, which are used to identify whether a person has difficulty functioning independently in activities of daily living, such as eating, managing money, dressing, moving, and getting along with others. Results of social-adaptive measures are used along with results of intelligence assessments to determine whether a label of intellectual disability is appropriate.

DS stands for Down syndrome, a genetic condition caused by the presence of an extra chromosome (chromosome 21). Sometimes the condition is described as Trisomy 21, and it virtually always results in delayed physical and mental development, however unlike what was believed in the past, a small percentage of individuals with Down Syndrome do not have intellectual disability. Also – thankfully – people with Down syndrome are no longer banished to institutions as they typically were in the past.

A percentile is a statistical concept which is based on the normal curve, and indicates the percent of individuals who score below any given score on a measure. For example, on a standardized test using 100 as the mean or average and 15 as the standard deviation, a score of 100 would be at the 50th percentile, meaning 50% of the scores would be below 100. A score of 85 would be at the 16th percentile, meaning 16% of the scores would be below 85, and a score of 70 would be at the 3rd percentile, meaning 3% would score below 70. Similarly, a score of 115 would be at the 84th percentile, and a score of 130 would be at the 97th percentile.

Reporting results in terms of percentiles allows comparisons of results on different types of assessment instruments. For example, Scholastic Aptitude Test results are often reported in percentiles, where a score of 1,030 is around the 50th percentile, a total score of 1,530 is around the 99th percentile, and a total score of 860 is around the 25th percentile.

A simplified definition of a standard deviation is that it is a statistical measure that indicates how much variation there is in scores on various measures, and what percentage of results fall between various scores. Many standardized instruments are constructed so that 15 is the standard deviation, with the mean or average score being 100. This means that a score of 85 is “one standard deviation below the mean” and a score of 115 is “one standard deviation above the mean.” Reporting scores in this way allows comparison of scores across different instruments and different points in time.

TBI stands for Traumatic Brain Injury. TBI is defined as brain injury that results from a blow or bump to the head, or from something piercing the brain, such as a bullet. TBI ranges from mild to severe, and the consequences can be short-term or long-term. Symptoms are varied and range in severity from headache to loss of consciousness and coma. TBI’s often cause difficulties in learning or retaining information, as well as changes in mood, sleep patterns, and emotions. This article on the Mayo Clinic has a good summary of TBI issues: https://www.mayoclinic.org/diseases-conditions/traumatic-brain-injury/symptoms-causes/syc-20378557

Self-advocacy refers to people with I/DD knowing their own strengths and challenges, and speaking up to communicate those to others, including participating actively in planning their own treatment, and making decisions about their lives.

Person-first language means that when we refer to someone with a disability or condition (not just an I/DD), we literally refer to the person before referring to the disability or condition. For example, we say a person with cancer, child with an intellectual disability, person with a TBI, or individual on the autism spectrum.