Mental Retardation: Definition, Classification, and Systems of Supports (10th ed.). Ruth Luckasson, Sharon Borthwick-Duffy, Wil H. E. Buntinx, David L. Coulter, Ellis M. (Pat) Craig, Alya Reeve, Robert L. Schalock, Martha E. Snell, Deborah M. Spitalnik, Scott Spreat, and Marc J. Tassé. Washington, DC: American Association on Mental Retardation, 2002.

Since its founding in 1876, the American Association on Mental Retardation (AAMR) has served a central role in understanding, defining, and classifying the condition known as mental retardation. The AAMR first published a manual on definition and classification in 1921. Updated editions have appeared periodically and have mirrored evolving perspectives on the nature, etiology, and functional consequences of mental retardation over the past 81 years. The most recent 10th edition of the Manual builds on this historical foundation and reflects an integration of commentary offered at numerous public forums with key findings in the literature on mental retardation since 1992 as well as input from AAMR members and advocates. The new Manual is the product of the careful synthesis of this information by the AAMR Ad Hoc Committee on Terminology and Classification.

The authors note that people who are labeled as having mental retardation and those who work with and advocate for this population are struggling to identify a new, less stigmatizing term for this disability. However, at this time no consensus has emerged among stakeholder groups for an acceptable alternative term that means the same thing. Consequently, the term mental retardation has been retained in the current 10th edition, although the authors do note that the term will likely change in the near future. Despite this caveat the current Manual reflects a synthesis of the state of our knowledge about mental retardation and provides both a definition and a wide ranging discussion of the implications of current understanding in relation to defining, classifying, and providing services to this population.

The 2002 AAMR definition of mental retardation is as follows:

Mental retardation is a disability characterized by significant limitations in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills. This disability originates before age 18.

According to the AAMR, five assumptions are essential to the application of the definition for the purposes of naming, defining, and classifying mental retardation:

  1. Limitations in present functioning must be considered within the context of community environments typical of the individual's age peers and culture.

  2. Valid assessment considers cultural and linguistic diversity as well as differences in communication, sensory, motor, and behavioral factors.

  3. Within an individual, limitations often coexist with strengths.

  4. An important purpose of describing limitations is to develop a profile of needed supports.

  5. With appropriate personalized supports over a sustained period, the life functioning of the person with mental retardation generally will improve.

The three prongs of this definition—significant limitations in intellectual functioning and in adaptive behavior, with onset before age 18—are retained from earlier AAMR definitions. The 9th edition of the AAMR Manual (1992) represented a significant paradigm shift in the conceptualization of mental retardation, from an absolute trait expressed solely by the individual to a mutable condition that results from on-going interactions between a person with limited intellectual functioning and the environment. The 1992 Manual also maintained that the meaning of mental retardation is functional and interactionist rather than statistical and proposed that classification be based on the intensity of needed supports rather than on the severity of impairment (i.e., mild, moderate, severe, and profound categories based on IQ scores). The current 2002 Manual maintains this strong commitment to a person-centered, ecological approach to definition and classification.

The AAMR 10th edition extends the functional approach to defining mental retardation and proposes an explicit, contextualist model to denote the relationships among individual functioning, supports, and social outcomes. According to the AAMR model, five dimensions of functioning are central to defining the impact of mental retardation on social outcomes: intellectual abilities; adaptive behavior; participation, interactions, and social roles; health; and context (e.g., environments, culture), and each of these dimensions is mediated through the supports available to the person. Thus, mental retardation is a “particular state of functioning in a particular context of time and place that results from interactions between individuals and their environments and interactions among risk factors across a lifetime” (p. 139).

The authors note that, from the earliest formal conceptualization of mental retardation to the present time, adaptive behavior deficits were the distinguishing feature of this disability. Despite this, the assessment of intellectual functioning has dominated the diagnosis of mental retardation, with a measured IQ being the primary and essential criterion. The AAMR 10th edition attempts to correct this imbalance by encouraging practitioners to focus on both intellectual functioning and adaptive behavior skills in the diagnosis and classification of this disability. The new Manual retains the perspective adopted in the 9th edition that adaptive behavior skills are particular and specific to domains of functioning rather than global and general. At the same time, the AAMR 10th edition eliminates reference to 10 adaptive behavior skill domains and adopts a tripartite model of adaptive behavior as a collection of conceptual, social, and practical skills. The 10th edition also eliminates the reference to problem or maladaptive behavior that was included as a dimension of adaptive behavior in previous editions. The authors note that the assessment of adaptive behavior skills should refer to an individual's performance of conceptual, social, and practical skills during daily routines, in typical environments, and under changing circumstances.

The AAMR 10th edition is divided into five sections that address the theoretical model, diagnosis, classification, supports, and implications. The first section of the Manual presents the new definition and the model that serves as its foundation. In chapter 1 the new definition is introduced and explicit operational definitions for key terms are provided (e.g., adaptive behavior, supports). Chapter 2 contains a detailed historical review of previous AAMR definitions as well as research-based findings published in the professional literature since 1992 and recent critiques of the 1992 definition. Chapter 3 includes a thorough discussion of the ecological model.

In the second section of the Manual, the authors address assessment issues in the diagnosis of mental retardation. It includes chapters on assessment of intellectual functioning (chapter 4) and adaptive behavior (chapter 5), as well as a discussion of the role of clinical judgment in the diagnostic process (chapter 6). This section also includes a review of the technical adequacy of contemporary instruments and key considerations for assessment of intellectual functioning and adaptive behavior. The third section of the Manual, in which issues related to classification of persons with mental retardation are addressed, includes chapters on the similarities and differences in various contemporary disability classification schemes (chapter 7), as well as etiology and prevention strategies and the relationship of these to supports (chapter 8). The fourth section of the Manual integrates current perspectives on support-based service provision with the focus on supports in the current AAMR definition. It includes chapters on the application of person-centered support strategies in the planning and provision of services (chapter 9), physical and mental health issues (chapter 10), and a discussion of public responsibility in the provision of supports (chapter 11). In the final section of the Manual (chapter 12), implications of the 2002 System for current practices in education and habilitation are discussed.

The AAMR 10th edition is a curious mixture of old and new perspectives on the disability of mental retardation. The authors retain the centrality of standardized intelligence tests in the diagnosis of mental retardation and note that intellectual functioning is “best represented by IQ scores that are obtained from appropriate assessment instruments” (p. 41). At the same time, they rightly acknowledge that even the best contemporary intelligence tests are generally more accurate for individuals who score closer to the mean score and are less accurate in classifying individuals who have extreme scores. Because all scores below the cutoff score of 70 can be considered extreme scores (i.e., at least two standard deviations below the mean) for which standardized intelligence tests have limited sensitivity, the authors of the 10th edition also emphasize the role of clinical judgment in the use of standardized assessments of intellectual functioning and adaptive behavior for the purpose of classifying individuals. At the same time, the new definition strongly reflects an ecological approach to disability that stresses the power of person–environment interactions and the reduction of functional and activity limitations through person-centered support strategies. The new definition is consistent with other contemporary models of disability such as the ICD-10, ICF, and DSM-IV as well as with eligibility guidelines for state developmental disability and Medicaid Waiver programs.

A second area of ambiguity in the new definition pertains to the role of supports in the diagnosis and classification of mental retardation. The definition emphasizes the central role of supports in determining the social outcomes that result from particular person–environment interactions and stresses that the evaluation of supports is a key aspect of defining and classifying mental retardation. On the one hand the definition eliminates the statistical approach to classification based on impairment categories ranging from mild to profound and proposes instead four broad categories, ranging from intermittent to pervasive, that reflect the intensity of support needs. However, the authors also state that the classification of supports are not intended to replace the familiar severity levels. Perhaps this ambiguity with regard to the use of the support model in diagnosis and classification is to be expected given the complexity of the multidimensional, contextual model that best embodies the state of our knowledge of mental retardation.

The authors of the 10th edition also acknowledge the systemic obstacles that continue to inhibit the adoption of a supports-based classification system in education and habilitation agencies. They note that a recent survey of directors of special education in 50 states indicated that most states continue to use the familiar IQ-based impairment categories as well as the 10 adaptive skill domains contained in the earlier 1983 definition. Also, the few states that have attempted to implement the 1992 definition misinterpreted support intensity levels as a substitute for levels of impairment. The limited implementation of the 1992 definition by schools and agencies most likely reflects the mismatch between the status of our knowledge and the state of our contemporary practices in the diagnosis and classification of persons with mental retardation. In this same manner, the 2002 Manual is forward-looking and oriented toward systems change and is not tailored for use by agencies and schools that may not be ready to adopt the person-centered support model that represents contemporary best practices in diagnosis, classification, and service provision.

The field of mental retardation continues to be in a state of flux, with spirited disagreements on numerous issues that are relevant to the AAMR goal of establishing an acceptable definition of this disability. For example, consensus remains illusive in regard to (a) the nature of intelligence, (b) the relationship between intelligence and adaptive behavior, (c) how to implement the person-centered support model, (d) the best way to characterize disabling conditions, and (e) the effects of terminology upon individual lives. Thus, the AAMR 10th edition is best understood as a work in progress that honestly reflects the present consensus of the field and discusses the issues around which consensus has yet to crystallize. The Manual makes an important contribution in its integration of contemporary perspectives and its adoption of a supports-based approach to diagnosis, classification, and service provision. The authors also perform an important service to the field through the thorough and comprehensive discussion of the theoretical foundation and practical implications of the new definition for understanding the condition of mental retardation and providing services to persons with this disability.