Abstract

The Diagnostic and Statistical Manual of Mental Disorders—Fifth Edition (DSM-5) diagnostic criteria for intellectual disability (ID) include a change to the definition of adaptive impairment. New criteria require impairment in one adaptive domain rather than two or more skill areas. The authors examined the diagnostic implications of using a popular adaptive skill inventory, the Adaptive Behavior Assessment System–Second Edition, with 884 clinically referred children (ages 6–16). One hundred sixty-six children met DSM-IV-TR criteria for ID; significantly fewer (n  =  151, p  =  .001) met ID criteria under DSM-5 (9% decrease). Implementation of DSM-5 criteria for ID may substantively change the rate of ID diagnosis. These findings highlight the need for a combination of psychometric assessment and clinical judgment when implementing the adaptive deficits component of the DSM-5 criteria for ID diagnosis.

The diagnosis of intellectual disability (ID; formerly known as mental retardation) is characterized by concurrent deficits in intellectual and adaptive functioning, with onset prior to adulthood. Prevalence rates for ID are generally estimated to be 1% of the population, with higher rates in middle and low-income countries (Maulik, Mascarenhas, Mathers, Dua, & Saxena, 2011). In the United States, this amounts to approximately 3 million people (Larson et al., 2001), with more than 543,000 children (ages 6–21) identified by the public school system as having some level of ID (U.S. Department of Education, 2007). A diagnosis of ID has a number of important implications, including eligibility for supports such as academic services, residential placement, vocational support, and Social Security Disability, as well as ineligibility for capital punishment.

The definition of ID has undergone many revisions. Initially, ID referred only to impairments in intellectual functioning; however, in 1959, impairments in age-appropriate day-to-day functioning (adaptive functioning) formally became part of the definition (Heber, 1959, 1961). More recent diagnostic formulations of ID have maintained the requirements for deficits in both intellectual ability and adaptive functioning. In the Diagnostic and Statistical Manual of Mental Disorders—Fourth Edition (Text Revision; DSM-IV-TR), the intellectual impairment component of the diagnosis of ID was defined as “significantly subaverage intellectual functioning: an IQ of approximately 70 or below” (American Psychiatric Association, 2000, p. 49). Based largely upon the definition of adaptive functioning proposed by the American Association of Intellectual and Developmental Disabilities (AAIDD, formerly known as the American Association on Mental Retardation; Luckasson et al., 1992), DSM-IV-TR defined adaptive functioning deficits as concurrent impairments (e.g., performance approximately 2 standard deviations [SD] below the mean) in at least two theoretically derived adaptive skill areas (i.e., communication, self-care, home living, social/interpersonal skills, use of community resources, self-direction, functional academic skills, work, leisure, health, and safety; American Psychiatric Association, 2000). Of note, there is some debate about whether there are 10 or 11 adaptive skill areas depending on whether or not health and safety are considered distinct skill areas. Subsequently, broader factors or adaptive domains composed of these individual adaptive skill areas were described (e.g., Greenspan, 1999; Harrison & Oakland, 2003; Luckasson et al., 2002; Thompson, McGrew, & Bruininks, 1999). These three broad domains (i.e., Conceptual, Social, Practical) have since been incorporated into the AAIDD description of adaptive functioning (Luckasson et al., 2002; Schalock et al., 2010).

The fifth edition of the DSM (DSM-5; American Psychiatric Association, 2013) includes a change in the name of the disorder, a revision of the diagnostic criteria, and changes in the severity specifiers. Consistent with the AAIDD's and the international community's shift from the term mental retardation to intellectual disability, DSM-5 uses the term intellectual disability coupled with the term intellectual developmental disorder (to be consistent with International Classification of Diseases, 11th Edition). As was the case with DSM-IV, DSM-5 diagnostic criteria for ID specify evidence of intellectual and adaptive impairment during the developmental period. DSM-5 criteria pertaining to intellectual impairment are similar to those of DSM-IV and stipulate deficits in “general mental abilities such as reasoning, problem-solving, planning, abstract thinking, judgment, academic learning, and learning from experience,” defined as an IQ of approximately ≤ 70 (± 5 points for error; American Psychiatric Association, 2013, p. 37). The DSM-5 criteria pertaining to deficits in adaptive functioning, however, have been more significantly modified. Specifically, adaptive impairment is defined as follows (American Psychiatric Association, 2013):

Deficits … that result in failure to meet developmental and sociocultural standards for personal independence and social responsibility (p. 33).…[The criterion] is met when at least one domain of adaptive functioning—conceptual, social, or practical—is sufficiently impaired that ongoing support is needed in order for the person to perform adequately in one or more life settings at school, work, home or in the community. (p. 38)

In contrast to DSM-IV, which stipulated impairments in two or more skill areas, DSM-5 criteria denote impairment in one or more superordinate domains of adaptive functioning (e.g., Conceptual, Social, Practical).

DSM-5 also redefines how ID severity is determined. DSM-IV-TR defined severity on the basis of IQ test scores (mild, moderate, severe, or profound). These same levels of severity are retained; however, in DSM-5 “the various levels of severity are defined on the basis of adaptive functioning, and not IQ scores, because it is adaptive functioning that determines the level of supports required. Moreover IQ measures are less valid in the lower end of the IQ range” (American Psychiatric Association, 2013, p. 33).

For diagnostic purposes under DSM-5, deficits in adaptive functioning are still established by way of clinical evaluation and administration of psychometrically sound measures, such as questionnaires that elicit observer or informant ratings of an individual's typical level of independent functioning (McCarver & Campbell, 1987). Of note, however, DSM-5 provides a table offering additional guidance for determining severity of adaptive impairment (i.e., mild, moderate, severe, and profound) within Conceptual, Social, and Practical domains. This table is intended to assist in determination of severity of adaptive impairment, although no specific guidance is given regarding the use of test scores for the determination of severity specifiers (e.g., the mild range of ID is not defined by a test score range). Clinicians are encouraged to use “both clinic evaluation and individualized, culturally appropriate, psychometrically sound measures” (American Psychiatric Association, 2013, p. 37), and to use clinical judgment when interpreting scores from these measures.

One such standardized observer–informant report instrument is the Adaptive Behavior Assessment System—Second Edition (ABAS-II; Harrison & Oakland, 2003), which is a commonly used measure of adaptive functioning on which a caregiver rates the individual's level of independent functioning on multiple items across skill areas. The parent form is used for children ages 5–21 years and provides estimates of the child's functioning across 9 skill areas (or 10 skill areas if he or she is employed). Scale composition of the first edition of the ABAS (Harrison & Oakland, 2000) was substantively influenced by the definition of adaptive functioning proposed by the AAIDD and others (e.g., Luckasson et al., 1992; Thompson et al., 1999), as well as the diagnostic criteria in DSM-IV. The skill areas were maintained in the publication of the second edition (ABAS-II; Harrison & Oakland, 2003), but in keeping with the existing body of research (e.g., Greenspan, 1999; Harrison & Oakland, 2003; Luckasson et al., 2002; Thompson et al., 1999) and the revised ID conceptualization proposed by the AAIDD, these skill areas were further organized into three broad adaptive skill domains: Conceptual, Practical, and Social. The ABAS-II domains have increased relevance with the publication of DSM-5, as they map onto the new adaptive domain model presented in DSM-5. Of note, the ABAS-II groupings of the individual skill areas into domain scales were modeled on theoretical foundations based in earlier research, and were not based on exploratory factor loadings. Subsequently, confirmatory factor analysis of the ABAS-II has yielded only modest support for this three-factor model (Wei, Oakland, & Algina, 2008), and there is evidence to suggest that the most parsimonious fit to the data is a one-factor solution (Harrison & Oakland, 2003). To date, there has been little research on the appropriateness of the 9 and 10 skill area factors.

The aim of this study was to examine the potential impact of the DSM-5 diagnostic criteria on classification rates of ID. There is the potential for a “gray zone” in which individuals meet ID criteria under the DSM-IV-TR criteria (i.e., impairment in two or more skill areas) but not under DSM-5 criteria (i.e., impairment in one or more domains), particularly when psychometric measures such as the ABAS-II are used as the primary means to quantify deficits in adaptive functioning. For instance, under the ABAS-II factor structure, individuals with skill deficits in home living and self-care might still qualify for ID, as both of these skills are grouped under the Practical domain factor. In contrast, an individual with skill deficits in social skills and functional communication might not, as these skill areas are grouped into different domain factors. Clarification of a possible diagnostic drift in ID diagnoses is valuable, as the implications for the educational (i.e., eligibility for special education services), social (i.e., eligibility for entitlement services and funding), and legal (i.e., capital punishment decisions) systems may be profound. To this end, we examined ID classification rates using a psychometric definition of impairment as two or more skill areas (DSM-IV-TR criteria) and one domain area (DSM-5 criteria), with adaptive impairment defined as standardized scores ≥ 2 SD below the mean. Given persistent questions about the factor structure of the ABAS-II, we hypothesized that, when compared with classification rates of ID using DSM-IV-TR criteria, diagnosis based on psychometrically defined impairment in one domain (DSM-5 criteria) has the potential to result in significantly fewer children meeting criteria for ID.

Methods

Participants

For the purposes of this study, de-identified patient records from the clinical database of the Department of Neuropsychology at the Kennedy Krieger Institute, a large medical institute serving youth with developmental disabilities in the mid-Atlantic region, were reviewed. Data are routinely entered into this database by department clinicians via the electronic health record, and are securely maintained by the information systems department. After approval by the Johns Hopkins Hospital institutional review board, a limited dataset was constructed of patients between the ages of 6 and 16 years for whom valid scores on both intellectual (e.g., Wechsler Intelligence Scales for Children—Fourth Edition, WISC-IV; Wechsler, 2003) and adaptive (e.g., ABAS-II; Harrison & Oakland, 2003) measures were available. The final sample included 884 children (mean age  =  10.49, SD  =  2.80; 67% male), for whom records included WISC-IV and ABAS-II scores, age at time of assessment, ethnicity, and sex. All patients included in the dataset had been referred for outpatient neuropsychological assessment. Of these 884 children and adolescents, 203 had a Full Scale IQ (FSIQ) that was ≥ 2 SD below the mean (FSIQ ≤ 70), representing 23% of the total clinically referred sample.

Measures

ABAS-II

The ABAS-II is a parent-report questionnaire assessing whether an individual independently displays the functional skills necessary for age-appropriate daily living. The ABAS-II divides adaptive functioning into nine skill areas, which are subsumed under three theoretically derived domains: the Conceptual Domain (Communication, Functional Academics, and Self-Direction skill areas), Social Domain (Leisure and Social skill areas), and Practical Domain (Community Use, Home Living, Health and Safety, and Self-Care skill areas). A 10th skill area, Work skills, can be administered to older adolescents and young adults who are employed, but it was not included in this study given the age range of the sample. The nine primary skill areas can be used to generate a General Adaptive Composite (GAC). As noted in the test manual (Harrison & Oakland, 2003), the ABAS-II GAC has strong internal consistency (α  =  .98) as do the domain (α  =  .86–.93) and skill area scores (α  =  .95–.97). Stability over time (M  =  12 days, SD  =  10 days) is strong (GAC corrected test–retest reliability r  =  .93, domain corrected test–retest r  =  .89–.93, skill area corrected test–retest r  =  .84–.92). The ABAS-II also has demonstrated adequate validity in a sample of children with ID (e.g., mean GAC scores in a group of 41 individuals between the ages of 5 and 21 diagnosed with ID, of unspecified severity, was equal to 63.7, mean skill area scaled scores ranged from 3.7 to 5.5). Of note, 82.93% of these individuals with ID had two or more individual skill area scores that fell at or below −2 SD, while 80.49% of these same individuals had one or more adaptive domain scores that fell at or below −2 SD based on caregiver report. Because the sample is described as “unspecified,” there is no way to examine these data at various levels of intellectual impairment (e.g., mild versus moderate intellectual ability). However, although statistical significance was not reported, there was a trend toward a higher percentage of impaired skill area scores reported for individuals with mild ID in the validity data for the teacher version of the ABAS-II. Specifically, of the 66 individuals with mild ID who were rated by their teachers on the ABAS-II, 75.76% had two or more individual skill areas scores that fell at or below −2 SD, while only 60.61% of these same individuals had one or more adaptive domain scores that fell at or below −2 SD (Harrison & Oakland, 2003).

Two other commonly used measures of adaptive functioning are the Vineland Adaptive Behavior Scales, Second Edition (VABS-II; Sparrow, Cicchetti, & Balla, 2005) and the Scales of Independent Behavior, Revised (SIB-R; Bruininks, Woodcock, Weatherman, & Hill, 1996). Correlations between the ABAS-II GAC and VABS-II Adaptive Behavior Composite were moderately high (r  =  .78), with correlations at the subdomain/skill area level mostly falling in the 0.50 range. Correlations between the ABAS-II GAC parent version and the Early Development Form of the SIB-R Broad Independence Score were low (r  =  .18), while the correlation between the ABAS-II GAC teacher-version and the Short Form of the SIB-R Broad Independence Score were stronger (r  =  .59).

WISC-IV

The WISC-IV is a widely accepted measure of intellectual ability with adequate psychometric properties for identifying children with ID. The WISC-IV provides a global intellectual estimate, the FSIQ. The FSIQ has shown excellent internal reliability and stability over time (e.g., internal consistency estimates [split-half] yield an FSIQ r  =  .97; corrected test–retest r  =  .93). The WISC-IV FSIQ also has demonstrated adequate validity for use with this population (Wechsler, 2003).

Experimental Design

First, we examined the pattern of associations between measures of intellectual and adaptive skill areas. Next, the total number of children who met strict DSM-IV-TR criteria for ID was identified (i.e., WISC-IV FSIQ ≤ 70, with two or more skill areas on the ABAS-II ≤ scaled score of 4). The total number of children who met the psychometrically defined DSM-5 criteria was then calculated (i.e., WISC-IV FSIQ ≤ 70, with one or more domains on the ABAS-II ≤ 70). The McNemar test was used to compare the differences in the proportion of individuals classified as ID based on the changing criteria for adaptive impairment.

Results

Of the 203 children with FSIQ ≤ 70, 166 met DSM-IV-TR criteria for adaptive impairment, that is, impairment in two or more skill areas. On the basis of DSM-5 criteria for adaptive impairment (i.e., impairment in one or more adaptive domains), 151 children met criteria for ID. This represents a net loss of 15 children. Sixteen children met DSM-IV-TR criteria but not DSM-5 criteria, and one child met DSM-5 criteria but did not meet DSM-IV-TR criteria. This net difference of 15 children represents a statistically significant 9% decrease in the number of children who met criteria for ID under DSM-5 as compared to DSM-IV-TR (McNemar test χ2  =  122.02, p  =  .001). Mean scores on the ABAS-II and WISC-IV for the children who meet DSM-IV-TR and DSM-5 criteria for adaptive impairment are presented in Table 1.

In the total clinically referred sample (N  =  884), there was a broad range of correlations between FSIQ and individual skill areas on the ABAS-II. The strongest correlations were noted between FSIQ and the ABAS-II Functional Academics (r  =  .56, p < .001) and Communication (r  =  .39, p < .001) skill area scales. All of the remaining seven ABAS-II skill area scales also were significantly correlated with FSIQ (p < .001), with correlations ranging from r  =  .13 to r  =  .32. Each of the composite domain scales of the ABAS-II was significantly correlated with FSIQ (all p < .001), with the strongest correlations noted with the Conceptual domain (r  =  .48) as compared to the Social (r  =  .31) and Practical (r  =  .32) domains. In children with FSIQ ≤ 70, the frequency of impaired scores (i.e., scaled score ≤ 4) on the ABAS-II skill area scales was as follows: Home Living (70%), Self-Direction (68%), Social (66%), Functional Academics (58%), Self-Care (56%), Community Use (51%), Communication (46%), Health and Safety (45%), and Leisure (35%). In this group, impaired domain scores (standard scores ≤ 70) were most frequently found on the Conceptual (62%) and Practical (62%) composites and were less frequently observed on the Social composite (48%).

Data on the 17 children whose status changed with the shift to DSM-5 criteria are presented in Table 2. Bold font is used to denote children who were impaired in ABAS-II skill areas. The one child who met DSM-5, but not DSM-IV, criteria was impaired on the Conceptual domain and had a single area of skill area impairment (Communication), with three other skill areas in the borderline-impaired range. Of the 16 children who met DSM-IV, but not DSM-5, criteria, 100% had a FSIQ of ≤ 70, 25% had a Verbal Comprehension Index of ≤ 70, 38% had a Perceptual Reasoning Index of ≤ 70, 81% had a Working Memory Index of ≤ 70, and 88% had a Processing Speed Index of ≤ 70. The majority of these children had two skill areas impaired (69%), with 19% impaired on three skill areas, and 12% impaired on four skill areas. Home Living was most likely to be impaired (56%), followed by Communication (38%), Functional Academics (38%), Self-Care (31%), Social (31%), Self-Direction (19%), Community Use (19%), and Health & Safety (12%). No children were impaired on Leisure.

Discussion

This study sought to investigate any potential impact on the rates of ID classification when an existing and widely used adaptive functioning measure (ABAS-II) was used to psychometrically determine deficits in adaptive functioning based on implementation of the new DSM-5 ID criteria. The DSM-5's use of adaptive impairment to quantify severity of ID highlights a renewed emphasis on adaptive functioning in this condition. There is concern, however, that the diagnostic change from adaptive skill deficits to adaptive domain deficits might make the diagnosis more restrictive due to instrumentation and measurement issues, particularly when psychometric measures are used as the primary means to quantify deficits in adaptive functioning. We hypothesized that, when using the ABAS-II to psychometrically quantify adaptive impairment, fewer children would qualify for an ID diagnosis when DSM-5 criteria were implemented (relative to DSM-IV). This was supported, as we identified a potential 9% decline in the number of children who met criteria for DSM-5 as compared with DSM-IV-TR in our large clinical sample. Of note, the children excluded by DSM-5 ID criteria had milder degrees of adaptive impairment, although their profiles still indicated a high level of adaptive and intellectual impairment. Given the relatively mild nature of their adaptive impairment, it is unclear whether these children and adolescents would have been identified with ID during the DSM-IV-TR era, even though their IQ and ABAS-II scores were consistent with the diagnostic criteria. As such, these data are of somewhat limited value in anticipating the true impact of DSM-5 on rates of ID. What these data do highlight, however, is the need for clinical judgment when interpreting these scores, rather than a strict reliance upon scores from the current psychometric scale compositions.

When adaptive impairment is psychometrically defined using ABAS-II scores, the children in our sample who would be “left out” of an ID diagnosis by the impaired domain criterion still show compelling evidence of intellectual and adaptive skill impairment. Among the children left out of the DSM-5 ID classification, their various combinations of adaptive skill area deficits tended to load onto different domains (rather than a single domain), resulting in domain level scores that were above a standard score of 70 in spite of the presence of impairment in multiple skill areas. For instance, a child with skill area deficits in Communication, Social skills, and Community Use may experience significant adaptive impairment, even though each of these skill areas is grouped onto separate ABAS-II domains and these composite scores may fall within normal limits. Analysis of adaptive functioning in the 16 children who would be excluded from an ID diagnosis based on DSM-5 criteria revealed that Home Living was the most commonly impaired skill area, followed by Communication, Functional Academics, Self-Care, and Social skills. These skill areas span all three of the ABAS-II adaptive domains, and highlight the manner in which significant skill area deficits may be hidden by grossly intact domain scores.

Given the common assumption that intellectual deficits contribute to deficits in adaptive skills in youths with ID, it is not unexpected that intellectual and adaptive functioning would be significantly correlated. From a measurement perspective, however, it remains unclear whether a low score in an adaptive area that is highly correlated with IQ constitutes a distinct area of adaptive deficit related to IQ rather than simply a multimethod approach to measuring the same construct. This has, in fact, been a criticism of the formulation of the diagnosis of ID in the past, as Greenspan (2006) and others have proposed that the Conceptual composite of the ABAS-II and its constituent skill area scales may measure much the same construct as an IQ test (i.e., conceptual or academic intelligence). Indeed, in our sample of children with a FSIQ of ≤ 70, IQ was most highly correlated with the Conceptual domain (r  =  .30, p < .001), with smaller, albeit still significant, correlations with the Practical (r  =  .27, p < .001) and Social (r  =  .18, p < .001) domains. As noted, the degree of variation in correlation between IQ and adaptive domain scores not only raises a concern regarding multimethod assessment of the same construct (e.g., IQ and Conceptual adaptive functioning), but also raises a question as to the relatedness of IQ and adaptive functioning in general. While each ABAS-II adaptive domain was significantly correlated with IQ, the varying degrees of correlation between IQ and the three adaptive domains brings into question the idea of a direct relationship, which is presumed in the ID diagnosis (i.e., “To meet diagnostic criteria for intellectual disability, the deficits in adaptive functioning must be directly related to the intellectual impairments…,” American Psychiatric Association, 2013, p. 38).

Future conceptualizations of ID may benefit from further shifting the diagnostic emphasis to deficits in adaptive functioning, as this might better define a subgroup of individuals who are highly vulnerable to exploitation or injury and require additional protections (regardless of IQ). Barkley and colleagues have proposed the concept of adaptive disability, in which deficits in adaptive functioning are associated with behavioral factors (e.g., conduct problems, inattention, aggression) within the context of broadly intact intelligence (Barkley et al., 2002; Shelton et al., 1998). Other recent work has identified relatively distinct cognitive–behavioral clusters associated with deficits in adaptive functioning, with IQ representing only one of many variables thought to contribute to deficits in adaptive functioning (Papazoglou, Jacobson, & Zabel, 2013a). We propose that future DSM revisions consider the evidence for the concept of an adaptive disability in which deficits in adaptive functioning are the primary diagnostic feature, with associated specifiers to qualify presumed etiologies (e.g., with intellectual deficits, with executive functioning deficits, with affective dysregulation, etc.).

In closing, we strongly recommend that discussion concerning the impact of new DSM-5 ID diagnostic criteria include discussion of practical assessment issues that may occur when new diagnostic criteria are implemented using existing test instruments such as the ABAS-II. First, although existing adaptive skill instruments have been shown to be reliable, it is very important that the underlying construction of the tests be considered when they are applied to new diagnostic formulations. As noted earlier, the domain factor structure of the ABAS-II was organized on the basis of theoretical foundations, and the model then underwent confirmatory factor analysis. Although this is an appropriate method for test construction, it may not capture the strongest factor loadings or provide information about other potential arrangements of the scales. Subsequently, individual adaptive skill area deficits may be somewhat “silenced” in the larger factor model. As such, the diagnostic utility of existing adaptive skill instruments such as ABAS-II should be explored before presuming that they are equally valid under both DSM-IV-TR and DSM-5 conditions, and clinical judgment should continue to be emphasized in the diagnostic process to help minimize possible psychometric measurement issues. Moreover, agreement between different measures should be explored, as quantification of deficits in adaptive functioning can vary considerably between instruments (Papazoglou, Jacobson, & Zabel, 2013b) and further complicate the diagnostic picture. To mitigate the potential impact of these issues, DSM-5 recommends that the clinician use multiple sources of information as well as clinical judgment when establishing whether an individual presents with significant deficits in adaptive behavior.

In addition, we recommend that the appropriateness of content from current adaptive skill instruments be reviewed, particularly given the renewed emphasis placed on adaptive impairment in the DSM-5 ID diagnostic formulation. Due to the pace of accommodative technology, the definition of an adaptive deficit is likely to continue to change rapidly. Although the advent of GPS guidance systems, text-to-speech software, smart phones, electronic cueing devices, and other technologies has created exciting new habilitation opportunities, the speed with which these devices become available outpaces the more time-intensive process necessary for the development and standardization of adaptive skill measures. This dilemma will likely continue, creating a disparity between the reality of the individual's situation (e.g., ability to use a smart phone and access the Internet) and the content of the latest version of a standardized adaptive skill instrument (e.g., ability to use a pay phone and read a newspaper). Lack of items reflecting an individual's ability to use technologies such as a smart phone, a computer, and the Internet creates both face validity and content validity questions, particularly as these types of technologies continue to become normal, necessary components of daily living rather than accommodative technologies or interventions. This is a particularly salient dilemma for the ABAS-II, which contains the same item content from the original ABAS, which was developed prior to the collection of standardization data between December 1998 and December 1999.

Although these findings have important implications for clinical practice and policy, this study has several limitations. All children were clinically referred, so results may not be consistent with potential findings in a nonreferred population, although it is worth noting that the decision-making process regarding classification of ID is inherently a clinical one. More specifically, however, the Kennedy Krieger Institute is an internationally recognized center of excellence for children with developmental disabilities, thus the population of children referred for evaluation here may be more significantly impaired than those for whom ID classification decisions are made in other settings (e.g., local school special education decisions). If this is indeed the case, the measurement issues raised concerning the ABAS-II skill area and adaptive domain scores may be overrepresented or underrepresented. More research is needed regarding the factor structure of the ABAS-II and whether the 9 and 10 skill areas and three domains represent appropriate factor groupings of the ABAS-II items. Research to date has shown only modest support for the three domains (Wei et al., 2008), and there are limited data on the 9-and-10 factor solutions. No data were available regarding whether clinicians actually made a diagnosis of ID for all 166 children who met formal DSM-IV-TR criteria, and, to our knowledge, there are no published data examining how consistently clinicians adhered to DSM-IV-TR diagnostic criteria when making a diagnosis of ID. Nevertheless, these findings suggest a risk of fewer ID diagnoses when existing adaptive functioning instruments are used as the primary means by which to implement DSM-5 criteria for adaptive impairment.

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Author notes

Aimilia Papazoglou, Children's Healthcare of Atlanta; Lisa A. Jacobson, Kennedy Krieger Institute; Marie McCabe, Saratoga Springs, NY; Walter Kaufmann, Boston Children's Hospital; T. Andrew Zabel, Kennedy Krieger Institute.