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The contemporary view of intellectual and developmental disabilities: Implications for psychologists.

Psychologists are involved in the diagnosis, classification, and planning supports for persons with intellectual disability (ID) and closely related developmental disabilities (DD). The field of intellectual and developmental disabilities (IDD) is currently experiencing a significant transformation. This transformation encompasses an increasingly integrated approach to IDD, especially regarding shared aspects such as limitations in human functioning (i.e., disability), a focus on the human and legal rights of persons with a disability, the eligibility for services and supports based on significant functional limitations in major life activity areas, and an emphasis on individualized supports provided within inclusive community-based environments. Accompanying this transformation is the increased precision in both the operational definitions of IDD-related constructs, and the terminology used to describe the respective construct (Luckasson & Schalock, 2013; Schalock & Luckasson, in press; Schalock, Luckasson, Tasse, & Verdugo, 2018; Schalock & Verdugo, 2012). The reader is encouraged to study Tables 1 and 2 prior to reading the article to fully understand the operational definitions and associated terminology for each of these constructs.

The purpose of this article is to provide psychologists with the current definitions of intellectual disability, operational definitions of intellectual and developmental disabilities constructs, and the parameters of an integrated approach to disability. The article also discusses the implications of the above to psychologists who are involved in the diagnosis, classification, and/or planning supports to persons with IDD.

Current definitions of intellectual disability

Therearecurrentlythreeclosely aligned definitionsof intellectual disability (ID). The authoritative definition is that of the American Association on Intellectual and Developmental Disabilities (AAIDD). The AAIDD definition is that, "intellectual disability is characterized by significant limitations both in intellectual functioning and adaptive behavior as expressed in conceptual, social, and practical adaptive skills. This disability originates before age 18" (Schalock et al., 2010, p. 1). Closely aligned with this definition is that proposed in DSM-5 by the American Psychiatric Association (APA, 2013) which is that "intellectual disability (intellectual developmental disorder) is a disorder with onset during the developmental period that includes both intellectual and adaptive behavior deficits in conceptual, social, and practical domains" (p. 33). The third definition is found in ICD-11 (World Health Organization, 2018), which is that, "disorders of intellectual development are a group of etiologically diverse conditions originating during the developmental period characterized by significantly below average intellectual functioning and adaptive behavior that are approximately two or more standard deviations below the mean (approximately less than the 2.3 (rd) percentile), based on appropriately normed, individually administered standardized tests. Where appropriately normed and standardized tests are not available, diagnosis of disorders of intellectual development requires greater reliance on clinical judgment based on appropriate assessment of comparable behavioural indicators."

Although the wording used in the definition of ID has changed somewhat over the last 50+ years, what has not changed in these definitions is the emphasis on significant deficits in intellectual functioning and adaptive behavior, age of onset during the developmental period, and the correlational and not causative relation between intellectual functioning and adaptive behavior (Tasse, Luckasson, & Schalock, 2016). What has changed in these definitions and their application are: (a) terminology that has evolved from mental deficiency and mental retardation to intellectual disability; (b) an increasing acceptance of the equal weight given to adaptive behavior and intellectual functioning in the diagnosis of ID; (c) a better understanding of the factor structure of adaptive behavior (i.e., conceptual, social, and practical adaptive skills); (d) the use of the 95% confidence interval to establish the range of scores within which the individual's true score falls; and (e) an increased use of a subclassification system based on the person's needs for supports rather than the individual's intelligence quotient (IQ) level. These changes reflect a better understanding of intelligence and adaptive behavior; advances in the conceptualization and measurement of intellectual functioning and adaptive behavior; advances in understanding measurement error and score interpretation; and the expanded use of the definition as a basis for supports planning and subgroup classification (Schalock & Luckasson, in press; Tasse et al., 2016).

Operational definitions of IDD-related constructs and associated terminology

Operational definitions

A construct is an abstract or general idea based on observed phenomena and formed by arranging parts or elements (Schalock et al., 2010). An operational definition explains a construct and establishes its meaning and boundaries. The terminology used in reference to the respective construct is determined by its operational definition. Since this article focuses on the constructs of disability, intellectual disability, developmental disability, developmental disabilities, and intellectual and developmental disabilities, it is important to psychologists to understand the similarities and differences among these constructs. Based on the work of Schalock and Luckasson (in press), operational definitions of each are presented in Table 1.

The operational definitions presented in Table 1 allow for the better understanding of both the similarities and overlapping nature among IDD-related constructs. As reflected in the operational definitions, similarities involve defining the construct in terms of significant functional limitations, and focusing on the multidimensionality of human functioning. As also noted, the constructs of intellectual disability and developmental disabilities overlap. Thus, some but not all people who meet the criteria for developmental disability are considered to have intellectual disability. However, intellectual disability and developmental disabilities are not completely overlapping constructs; the construct of developmental disabilities also includes people with physical disorders (such as cerebral palsy or spina bifida) and other disorders that emerge during the developmental period, such as those with Fetal Alcohol Disorder and Autism Spectrum Disorder who do not have co-occurring ID (AAIDD, 2018; Brown, Wehmeyer, & Shogren, 2017; Centers for Disease Control and Prevention [CDC], 2018; National Institute of Health [NIH], 2018; Williams, Wheeler, Linder, & Jacobs, 2017).

Associated terminology

There is confusion in the IDD field about what precise term or term combination should be used in particular circumstances. This confusion is reflected in the plethora of terms and term combinations currently found in the literature and in statutes. Examples include "people with IDD", "ID/DD", "IDD", "ID-DD", "conditions similar to or related to mental retardation (now intellectual disability)", "conditions similar to one of these conditions", "pervasive developmental disorder", and "children and adults with intellectual and developmental disabilities."

Selecting the correct terminology to use regarding a specific construct should be based on each construct's operational definition, and the circumstances in which the construct is used. The need to use correct terminology is paramount. Matching the terminology to the construct is essential for valid clinical decisions and recommendations, establishing eligibility criteria for services and supports, conducting research, communicating across disciplines, and implementing an integrated approach to IDD. Terminology consistent with the operational definitions presented in Table 1 is provided in Table 2. The table also includes examples of the term's use.

The operational definitions of IDD-related constructs presented in Table 1, and the terminology associated with each construct presented in Table 2, make significant contributions to clear thinking, the use of more precise terminology, and an integrated approach to IDD. Specifically, their use will enhance valid clinical decisions and recommendations; facilitate the establishment of eligibility criteria for services and supports; provide objective, measurable variables for research studies; and improve productive communication across disciplines and professionals within support teams. In addition, the understanding of the similarities, differences, and overlapping nature of the constructs of intellectual disability (ID) and developmental disabilities (DD) will foster an integrated approach to disability policy development, implementation, and evaluation. Finally, the recognition of the relation of intellectual disability and developmental disabilities to the construct of disability anchors these two constructs within the construct of disability, which internationally is considered to be the expression of limitations in individual functioning within a social context and represents a substantial disadvantage to the person. This anchoring will facilitate cross-national communication and help to establish standardized international terminology (Luckasson & Schalock, 2013).

The parameters of an integrated approach to disability

There are currently four perspectives that explain IDD. Each perspective explores the impacts of various factors influencing IDD, provides the basis for interventions and supports, and organizes relevant information into a usable form for increased understanding and as a basis for better recommendations and decisions. As described by Schalock, Luckasson, Tasse, and Verdugo (2018), these four perspectives approach IDD from a biomedical, psycho-educational, sociocultural, or justice perspective.

* The biomedical perspective emphasizes genetic and physiological factors that result in IDD.

* The psychoeducational perspective emphasizes intellectual, psychological/behavioral, and learning limitations associated with IDD.

* The sociocultural perspective emphasizes the interaction between people and the environments through which social meaning of IDD develops from society's common beliefs, behaviors, language, and events around people with IDD and the responses of individuals to the interaction.

* The justice perspective emphasizes that all individuals, including those with a diagnosis of ID or DD, have the same human and legal rights.

Although each of these four perspectives currently serves and will continue to serve important purposes, individually they do not explain the complexity of IDD, nor do they individually provide an integrated approach to understand IDD and guide efforts to mitigate its impact. The integrated approach to IDD described in this article involves four parameters: the locus of disability, risk factors leading to disability, systems of supports, and an explicit and systematic process for subgroup classification. Key aspects of each are described next.

Locus of disability

The essential concept underlying this parameter is the multidimensionality of human functioning. A multidimensional approach reflects the interactive nature of disability and the significant role that personal and contextual factors play in the expression of genes and brain development, the dynamic and reciprocal engagement among intellectual functioning, adaptive behavior, health, one's context and participation, and the size and complexity of the discrepancy between personal competence and environmental demands. This multidimensional approach to human functioning also incorporates the presumed causes of disability, such as gene-environmental interaction, brain development, health, functional limitations, societal conditions and arrangements, and government structures.

Risk factors leading to disability

The risk factors leading to disability can be integrated into types of risk factors and timing of risk factors. Types of risk factors include (a) biochemical factors related to biologic processes such as genetic disorders or poor nutrition, (b) neural or brain development disorders, (c) social factors related to social and family skills and interactions, (d) behavioral factors related to potentially causal behaviors such as dangerous (injurious) activities or parental substance abuse, and (e) educational factors related to the availability of learning opportunities and supports that promote intellectual development and the development of adaptive skills. Additionally, risk factors are related to societal attitudes, impoverished or segregated environments, social inequality, injustice, discrimination, or denial of rights.

The timing of risk factors involves those that occur during the prenatal, perinatal, or post-natal period. Prenatal factors include chromosomal disorders, poverty, parental drug use, or lack of preparation for parenthood. Perinatal factors include birth injury, lack of access to prenatal care, parental rejection of caretaking, or lack of knowledge about interventions and supports. Postnatal factors include traumatic brain injury, impaired child-caregiver interactions, child abuse and neglect, or delayed diagnosis.

Systems of supports

Supports are defined as resources and strategies that aim to promote the development, education, interests, and personal well-being of an individual and enhance that person's functioning (Thompson et al., 2009). Systems of supports involve choice and personal autonomy, inclusive environments, generic supports, and specialized supports.

* Choice and personal autonomy involves opportunities to make choices and exercise self-determination, and recognition as a person before the law, enjoying the legal capacity on an equal basis with individuals who do not have a disability. Choice and personal autonomy is facilitated through supported decision making.

* Inclusive environments are those that provide access to resources, information, and relationships, encourage growth and development and support people, and accommodate psychological needs related to autonomy, competence, and relatedness. Examples include supported employment, supported living, supported/inclusive education, and aging in place.

* Generic supports are those that are widely available to the general population, including natural supports, technology, prosthetics, life-long education, reasonable accommodation, dignity and respect, and personal strengths/assets (Lombardi, Claes, & Schalock, 2018).

* Specialized supports are professionally-based strategies and therapies (e.g. educational, medical, psychological, occupational therapy, physical therapy, speech therapy, psychiatric, nursing).

Subgroup classification framework and process

Classification is not a diagnosis. Classification is an optional post-diagnosis organizing process that provides an organized scheme for the categorization of various kinds of observations and measures as a way to organize information to better understand a person's needs. Classification involves the systematic arrangement into subgroups according to established criteria. Subgroup classification has to occur within an explicit framework and systematic process, serve an important purpose, be based on relevant information, be used to better understand the individual's needs, and focus on the person's functioning rather than on the severity of the individual's disability (Schalock & Luckasson, 2015).

An explicit subgroup classification framework is built around three primary purposes for subgroup classification. These are to describe the intensity of support needs, the extent of limitations in intellectual functioning, and the extent of limitations in conceptual, social, and practical adaptive skills. For each purpose, the systematic process for subgroup classification involves: (a) establishing the important purpose for the subgrouping; (b) aligning relevant data sets to the subgrouping's purpose; (c) describing the data driven procedures used to establish the subgroup classification categories employed; and (d) using empirically-based subgroup classification bands to establish the subgroup classification categories.

Using this framework and these components allows psychologists to align the subgroup classification of support needs to best practices. For example, for supports planning, the pattern and intensity of assessed support needs obtained from the administration of a standardized support needs scale can be used. If it is necessary to classify the intensity of the individual's support needs, the categories of intermittent, limited, extensive, or pervasive can be used, with their subgroup classification bands established on the basis of percentile scores that reflect the intensity of support needs. When the purpose of subgroup classification is to describe the extent of limitations in conceptual, social, and practical adaptive behavior skills, adaptive behavior scores obtained from a reliable, valid, individually administered, comprehensive standardized test that yields adaptive behavior scores in each of the following three adaptive behavior domains of conceptual, social, and practical can be used. Although being used less, when the purpose of subgroup classification is to describe the extent of limitations in intellectual functioning IQ scores obtained from a reliable, valid, individually administered, comprehensive standardized test that yields a full-scale IQ score can be used.

There are numerous advantages for implementing an integrated approach to IDD. Chief among these are that an integrated approach to IDD: (a) sensitizes individuals to the interactive nature of human functioning dimensions, systems of supports, and human functioning outcomes (Luckasson & Schalock, 2013); (b) causes clinicians to realize that they should do more than just diagnose and/or classify individuals with ID; rather, clinicians need to align the clinical functions of diagnosis, classification, and planning supports (Schalock & Luckasson, 2014); (c) provides a better understanding of the complexity of IDD, the specific risk factors associated with its manifestation, and effective prevention and mitigation strategies; (d) provides a holistic framework for policy development and best practices, including wrap-around interventions and supports that integrate traditional interventions with strength-based support strategies; and (e) encourages the use of subgroup classification systems that are purposeful and benefit the individual (Schalock, Luckasson et al., 2018).

Relevance to psychologists

The transformation that is occurring in the field of IDD is having a significant impact on psychologists and their involvement in diagnosis, classification, and planning supports to persons with an intellectual or developmental disability. As discussed in this article, for precise and accurate decisions and recommendations, it is critical for psychologist to: (a) assure that the required criteria for a diagnosis of ID or DD are met; (b) understand IDD related constructs and use precise terminology associated with each construct; (c) recognize the different perspectives that explain ID and DD; (d) use best practices in terms of providing systems of supports; and (e) approach subgroup classification as an optional post-diagnosis organizing scheme that is based on an explicit subgroup classification framework.

In conclusion, it is important that psychologists recognize that intellectual disability and closely related developmental disabilities are more than a biomedical dysfunction or a psychoeducational impairment that can be mitigated through interventions and supports. Although a person's functioning generally will improve when the proper supports are in place (Schalock et al., 2010), intellectual disability and related developmental disabilities are life-long conditions. These disabilities are also social constructs that are based on the interactions of people and their environments, the human and legal rights operating within those environments, and the roles people with IDD and their families play within society. Thus, psychologists need to go beyond their own single perspective, and incorporate the contributions of other perspectives on IDD. When this is done, an integrated approach to IDD will ultimately enhance a wider range of valued outcomes for the individual.

References

American Association on Intellectual and Developmental Disabilities (2018). Frequently asked questions on intellectual disability. Retrieved from https://aaidd.org/intellectual-disability/definition/faqs-on-intellectual-disability#.WjGbhXlG3RZ

Brown, I., Wehmeyer, M. L., & Shogren, K. A. (2017). What is meant by the terms intellectual disability and developmental disabilities. In M. L. Wehmeyer, I. Brown, M. Percy, K. A. Shogren, & W. L. A. Fund (Eds.). A comprehensive guide to intellectual disability and developmental disabilities (pp. 3-18). Baltimore: Paul H. Brookes.

Centers for Disease Control and Prevention (2018). Facts about developmental disabilities. Retrieved from https://www.cdc.gov/ncbddd/developmentaldisabilities/facts.html#ref

Developmental Disabilities Assistance and Bill of Rights Act Amendments of 2000, PL 106-402, 42U.S.C.SS 6000 et seq.

Lombardi, M., Claes, C, & Schalock, R. L. (2018). Elements of a system of supports: Results from an international Delphi study. Manuscript in preparation.

Luckasson, R., & Schalock, R. L. (2013). Defining and applying a functionality approach to intellectual disability. Journal of Intellectual Disability Research, 57, 657-668. doi: 10.1111/j. 1365-2788.2012.01575.x

National Institute of Health (2018). Intellectual and developmental disabilities. Retrieved from https://report.nih.gov/nihfactsheets/ViewFactSheet.aspx?csid=100

Schalock, R. L., Borthwick-Duffy, S. A., Bradley, V. J., Buntinx, W. H. E., Coulter, D. L., Craig, E. M., .... Yaeger, M. (2010). Intellectual disability: Diagnosis, classification, and systems of supports (11th ed.). Washington, DC: American Association on Intellectual and Developmental Disabilities.

Schalock, R. L., & Luckasson, R. (2014). Clinical judgment (2nd Ed.). Washington, DC: American Association on Intellectual and Developmental Disabilities.

Schalock, R. L., & Luckasson, R. (2015). A systematic approach to subgroup classification in intellectual disability. Intellectual and Developmental Disabilities, 53,358-366. doi: 10.1352/1934-9556-53.5.358

Schalock, R. L., & Luckasson, R. (in press). Intellectual disability, developmental disabilities, and the field of intellectual and developmental disabilities. In L. Master-Glidden, L. Mclntyre, & M. J. Tasse (Eds.), APA Handbook of Intellectual and Developmental Disabilities. Washington, DC: American Psychological Association Press.

Schalock, R. L., Luckasson, R, Tasse, M. I, & Verdugo, M. A. (2018). A holistic theoretical approach to intellectual disability: Going beyond the four current perspectives. Intellectual and Developmental Disabilities, 56, 79-89. doi: 10.1352/1934-9556-56.2.79

Schalock, R. L., & Verdugo, M. A. (2012). A leadership guide for today's disabilities organizations: Overcoming challenges and making change happen. Baltimore, MD: Brookes.

Tasse, M. J., Luckasson, R., & Schalock, R. L. (2016). The relation between intellectual functioning and adaptive behavior in the diagnosis of Intellectual Disability. Intellectual and Developmental Disabilities, 54(6), 381-390. doi: 10.1352/1934-9556-54.6.381

Thompson, J. R., Bradley, V. I, Buntinx, W. H. E., Schalock, R. L., Shogren, K. E., Snell, M. E., ...Yaeger, M. H. (2009). Conceptualizing supports and the support needs of people with intellectual disability. Intellectual and Developmental Disabilities, 47, 135-146. doi:10.1352/1934-9556-472.135

Williams, M. E., Wheeler, B. Y., Linder, L., & Jacobs, R. A. (2017). Evolving definitions of autism and impact on eligibility for developmental disabilities services: California case example. Intellectual and Developmental Disabilities, 55, 192-209. doi: 10.1352/1934-9556-55.3.192

World Health Organization (2018). ICD-11 for mortality and morbidity statistics. Retrieved from: https://icd.who.int/

Robert L. Schalock (1), Ruth Luckasson (2), and Marc J. Tasse (3)

(1) Hastings College (USA), (2) University of New Mexico (USA), and (3) The Ohio State University (USA)

Received: November 14, 2018 * Accepted: March 21, 2019

Corresponding author: Robert L. Schalock

Hastings College (Nebraska, Estados Unidos)

P.O. Box 285, WA99109-0285

Chewelah, Estados Unidos

e-mail: rschalock@ultraplix.com

doi: 10.7334/psicothema2019.119
Table 1
Operational definitions of disability-related constructs

Disability-related
construct           Operational definition

                    A significant functional limitation that: (a)
                    reflects an inability or constraint in both
                    personal functioning and the performance of
                    socially expected roles and tasks; (b) represents
Disability          a substantial disadvantage to the individual; (c)
                    is influenced by contextual variables, and (d) can
                    be mitigated (i.e., reduced or alleviated) through
                    interventions and supports, or by reducing barriers
                    that preclude opportunities, equity, and
                    inclusion (Luckasson & Schalock, 2013)
Intellectual        Significant limitations both in intellectual
Disability (ID)     functioning and in adaptive behavior as expressed
                    in conceptual, social, and practical adaptive
                    skills. This disability originates before age 18
                    (Schalock et al., 2010, p. 1) A severe, chronic
                    disability of an individual that: (a) is
                    attributable to a mental or physical impairment or
                    a combination of mental and physical impairments;
                    (b) is manifest before the individual attains age
                    22; (c) is likely to continue indefinitely; (d)
                    results in substantial functional
Developmental       limitations in 3 or more major life activity areas;
                    and (e) reflects the individual's need for a
Disability (DD)     combination and sequence of special,
                    interdisciplinary, or generic services,
                    individualized supports, and other forms of
                    assistance that are of lifelong or extended
                    duration and are individually planned
                    and coordinated (DD Act, Sec. 102. (8)(A))
Developmental       A term used to refer to "a group of conditions due
Disabilities (DDs)  to an impairment in physical, learning, language,
                    or behavior areas. These conditions begin during
                    the developmental period, may impact day-to-day
                    functioning, and usually last throughout a
                    person's lifetime" (CDC, 2018)
Intellectual and    The broader, combined field of intellectual
Developmental       disability and developmental disabilities
Disabilities
(IDD)

Table 2
Terminology consistent with the construct's operational definition

Construct                         How to use terminology that is
                                  consistent with the construct and its
                                  operational definition
Disability                        As a broad, generalized label for
                                  individuals who exhibit significant
                                  functional limitations that cause a
                                  substantial disadvantage to the
                                  person
Intellectual disability (ID)      As a diagnosis or label given to
                                  individuals who meet the criteria of
                                  significant limitations both in
                                  intellectual functioning and adaptive
                                  behavior as expressed in conceptual,
                                  social, and practical skills, and is
                                  manifest before age 18
Developmental disability (DD)     As a label based on a diagnosis or
                                  for those individuals who meet the
                                  criteria of severe, chronic
                                  disability as specified in Sec.102.
                                  (8)(A) of the
                                  DD Act of 2000 (see Table 1)
Developmental disabilities (DDs)  As a broad, non-categorical label for
                                  a chronic disability manifest before
                                  age 22 but limited to persons with a
                                  specific diagnosis OR for those
                                  whose disability (manifest before age
                                  22) results in substantial functional
                                  limitations in three or more major
                                  life activity areas and who require
                                  long-term services and supports
Intellectual and developmental    As a broader, combined field of
                                  intellectual disability and
                                  developmental
disabilities (IDD)                disabilities
Construct                         Examples of the term's use

Disability                        * A person with a disability (e.g.,
                                    "I have a disability")
                                  * A bounded field of study, policy
                                    development, service/ support
                                    provision, or research (e.g., the
                                    field of disability)
Intellectual disability (ID)      * A person with intellectual
                                    disability (e.g., "I have ID")
                                  * A bounded field of study, policy
                                    development, service/ support
                                    provision, or research (e.g., the
                                    field of intellectual disability)
Developmental disability (DD)     * -A person with a developmental
                                    disability (e.g. "I have a
                                    developmental disability"; "I have
                                    autism"; "I have Down syndrome")
                                  * A specialized field of study
                                    bounded by a precise etiology or
                                    similar support needs
                                  * A bounded field of study, policy
                                    development, service/ supports
                                    provision, or research (e.g.
                                    autism spectrum disorder, Down
                                    syndrome)
Developmental disabilities (DDs)  * "Individuals with developmental
                                    disabilities"
                                  * A bounded field of study, policy
                                    development, service/ support
                                    provision, or research (e.g., the
                                    field of developmental disabilities)
                                  * An administrative definition (e.g.,
                                    "Five percent of our state has
                                    developmental disabilities and 80%
                                    are receiving services and
                                    supports")
Intellectual and developmental    * Persons with intellectual and
disabilities (IDD)                  developmental disabilities
                                  * Children and adults with
                                    intellectual and developmental
                                    disabilities
                                  * A bounded field of study, policy
                                    development, services/ supports
                                    provision, or research (e.g. the
                                    field of IDD)
                                  * Organization names and journal
                                    titles where the focus is on both
                                    ID and DDs (e.g. AAIDD, Journal of
                                    Intellectual and Developmental
                                    Disabilities, American Journal of
                                    Intellectual and Developmental
                                    Disabilities
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Author:Schalock, Robert L.; Luckasson, Ruth; Tasse, Marc J.
Publication:Psicothema
Date:Jul 1, 2019
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