Written by Najwa Bashir

Generally referred to as intelligence, intellectual functioning encompasses a broad variety of mental abilities, including the capacity for logical thinking, practical intelligence (problem-solving), learning, language skills, and so on. It can take many different forms, including talents, behaviors, ideas, and emotions. Stated differently, the ability to comprehend and engage with reality on a global scale is referred to as intellectual functioning (Lee et al., 2023).

According to American Association on Intellectual and Developmental Disabilities (AAID) (Shogren & Turnbull, 2010), intelligence is an all-encompassing mental ability that includes planning, reasoning, problem-solving, abstract thought, understanding complicated concepts, efficient learning, and experience-based learning. A standardized measure of intelligence, specifically an IQ score of less than 70 (two standard deviations below the population mean of 100), has historically been used to define intellectual disability (formerly known as “mental retardation”).

This measure has also historically been used to describe significant deficits in functional and adaptive skills. The capacity to do age-appropriate everyday tasks is a component of adaptive skills. The American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) and the American Association on Intellectual and Developmental Disabilities (AAIDD) system are the two classification schemes used in the US for intellectual disability (ID). Both of these methods use the degrees of support required to help an individual reach their maximum potential for personal functioning to determine the severity of ID (Boat et al., 2015).

Intellectual Disability

Intellectual Disability, also referred to as Intellectual Developmental Disorder, is defined as having an IQ of less than 70 and deficits in adaptive behavior or everyday living abilities (such as eating, dressing, communicating, and participating in activities with others). Individuals with intellectual disabilities struggle with complex concepts and learn slowly. Reduced cognitive capacity, or intellectual disability, results in a variation in the rate and efficiency with which an individual learns, retains, and applies new information in comparison to the general population (Shree & Shukla, 2016).

According to DSM-5, Intellectual Disability is a class of developmental disorders marked by deficits of cognitive functions that are linked to learning, adaptive behavior, and skill constraints (Carulla et al., 2011).

Diagnostic Criteria for Intellectual Disability

The DSM-5 TR (APA, 2000) has outlined a specific diagnostic criteria related to Intellectual Disability. The following three criteria needs to be met for individuals to be diagnosed with an Intellectual Disability:

1. Shortcomings in intellectual abilities – as demonstrated by individual, standardized intelligence tests as well as clinical evaluation – including logical problem-solving, organizing, abstract judgment, scholastic learning, and acquiring knowledge from experience.
2. Deficiencies in adaptive functioning that lead to a failure to fulfil social and developmental norms about social responsibility and personal independence.Without continued assistance, the adaptive impairments make it difficult for the person to operate in a variety of settings, including the community, workplace, school, and home, as well as in one or more everyday tasks including social interaction, communication, and independent living.
3. Intellectual and adaptive deficiencies that appear at the beginning of the developmental stage.

Diagnostic Features of Intellectual Disability

The DSM-5 TR (APA, 2016) lists many diagnostic features of Intellectual Disability. These characteristics consist of the following:

1. Deficits in general mental abilities
2. Impairment in day-to-day adaptive functioning relative to peers who are matched for age, gender, and sociocultural background
3. Onset takes place at the stage of development.

Standardized cognitive tests, standardized neuropsychological tests, and standardized measures of adaptive functioning are used in conjunction with clinical examination to diagnose intellectual developmental disorders.

Testing for intelligence quotient (IQ) and deficiencies in adaptive functioning – a measure of a person’s capacity to manage the typical stresses of daily life – are two ways to assess intellectual functioning.

The requirement to evaluate intellectual functioning using standardized instruments that produce intelligence quotients (IQs) is acknowledged by both DSM-5 and ICD-10. The DSM-5 limits the use of IQ to determine ID, using a threshold of 65–75 (IQ 70± standard error of 5). On the other hand, the ICD-10 recommends an IQ of 70 in order to diagnose ID, and it uses a range of IQs to classify four severity levels: mild (IQ: 50–69), moderate (IQ: 35–49), severe (IQ: 20–34), and profound (IQ <20). The IQ score can be regarded as one of the clinical descriptors that are significant in defining the severity level, although the ICD-11 Working Group argued that severity levels for IDD should be based on a clinical description of the traits of each subcategory. As a result, the ICD-10 guidelines, which rely on IQ to determine the severity levels of ID as well as to diagnose the condition, should be used until ICD-11 is implemented (Kishore et al., 2019).

Furthermore, the DSM-5 TR stipulates that intellectual impairment must also arise throughout the developmental period, which is often understood to be before the age of 18.

Standardized intelligence tests, such the Stanford-Binet Intelligence Scales or the Wechsler Intelligence Scale for Children (WISC), are used to measure intellectual functioning. People who are diagnosed with intellectual impairment usually have an IQ of less than 70, which is regarded as severely below average. It is crucial to remember that adaptive functioning must also be considered in order to diagnose intellectual impairment; IQ levels alone are not sufficient in this regard.

The ability of an individual to autonomously carry out everyday tasks and adjust to novel circumstances is referred to as adaptive functioning. This encompasses interpersonal, communication, self-care, and problem-solving abilities. Adaptive functioning deficits might show themselves as trouble with personal grooming, money management, or social cue interpretation.

Apart from intellectual and adaptive functioning deficiencies, the DSM-5 TR highlights the need of taking into account the cultural background and personal strengths and limitations of the individual undergoing assessment for intellectual impairment. When diagnosing someone, it is important to take into account many factors that may affect their performance on standardized tests, such as cultural differences, poverty, and limited access to education.

It is also critical to acknowledge that intellectual impairment can range in degree from moderate to severe. Even though they can struggle in school or with social skills, people with modest intellectual disabilities are typically able to live freely with assistance. To achieve their everyday requirements, those with moderate to severe intellectual disabilities can need close monitoring and assistance.

Conclusion

In conclusion, deficiencies in intellectual and adaptive functioning that begin throughout the formative stage are among the diagnostic characteristics of intellectual impairment as listed in the DSM-5 TR. When evaluating a patient for intellectual impairment, physicians should take into account the patient’s strengths and limitations, cultural influences, and cognitive and practical functioning. In order to help people with intellectual disabilities realize their full potential and enhance their quality of life, early detection and intervention are essential.

References

American Psychiatric Association. (2016). Diagnostic and statistical manual of mental disorders. Text revision.

Boat, T. F., Wu, J. T., & National Academies of Sciences, Engineering, and Medicine. (2015). Clinical characteristics of intellectual disabilities. In Mental disorders and disabilities among low-income children. National Academies Press (US). Available at: https://www.ncbi.nlm.nih.gov/books/NBK332877/

Carulla, L. S., Reed, G. M., Vaez-Azizi, L. M., Cooper, S. A., Leal, R. M., Bertelli, M., …&Saxena, S. (2011). Intellectual developmental disorders: towards a new name, definition and framework for “mental retardation/intellectual disability” in ICD-11. World Psychiatry, 10(3), 175. https://doi.org/10.1002/j.2051-5545.2011.tb00045.x

Kishore, M. T., Udipi, G. A., &Seshadri, S. P. (2019). Clinical practice guidelines for assessment and management of intellectual disability. Indian journal of psychiatry, 61(Suppl 2), 194-210. https://doi.org/10.4103/psychiatry.IndianJPsychiatry_507_18

Lee, K., Cascella, M., &Marwaha, R. (2023). Intellectual disability. Available at: https://www.ncbi.nlm.nih.gov/books/NBK547654/

Shogren, K. A., & Turnbull, H. R. (2010). Public policy and outcomes for persons with intellectual disability: extending and expanding the public policy framework of AAIDD’s 11th Edition of Intellectual Disability: Definition, Classification, and Systems of Support. Intellectual and Developmental Disabilities, 48(5), 375-386. https://doi.org/10.1352/1934-9556-48.5.375

Shree, A., & Shukla, P. C. (2016). Intellectual Disability: Definition, classification, causes and characteristics. Learning Community-An International Journal of Educational and Social Development, 7(1), 9-20. https://doi.org/10.5958/2231-458X.2016.00002.6

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