The Vineland Adaptive Behavior Scales: Supplementary Norms for Individuals with Autism

Transcription

1 Journal of Autism and Developmental Disorders, Vol. 28, No. 4, 1998 The Vineland Adaptive Behavior Scales: Supplementary Norms for Individuals with Autism Alice S. Carter,1,9 Fred R. Volkmar,2 Sara S. Sparrow,2 Jing-Jen Wang,3 Catherine Lord,4 Geraldine Dawson,5 Eric Fombonne,6 Katherine Loveland,7 Gary Mesibov,8 and Eric Schopler8 Vineland Adaptive Behavior Scales Special Population norms are presented for four groups of individuals with autism: (a) mute children under 10 years of age; (b) children with at least some verbal skills under 10 years of age; (c) mute individuals who are 10 years of age or older; and (d) individuals with at least some verbal skills who are 10 years of age or older. The sample included 684 autistic individuals ascertained from cases referred for the DSM-IV autism/pdd field trial collaborative study and five university sites with expertise in autism. Young children had higher standard scores than older individuals across all Vineland domains. In the Communication domain, younger verbal children were least impaired, older mute individuals most impaired, and younger mute and older verbal individuals in the midrange. Verbal individuals achieved higher scores in Daily Living Skills than mute individuals. The expected profile of a relative weakness in Socialization and relative strength in Daily Living Skills was obtained with age-equivalent but not standard scores. Results highlight the importance of employing Vineland special population norms as well as national norms when evaluating individuals with autism. KEY WORDS: Vineland Behavior Scales; special population norms; autism. INTRODUCTION This paper presents special population norms on the Vineland Adaptive Behavior Scales for individu- 1Departmenl of Psychology and Yale School of Medicine Child Study Center, New Haven, Connecticut. 2Yale School of Medicine Child Study Center and Yale University Department of Psychology, New Haven, Connecticut. 3American Guidance Service, Minneapolis, Minnesota. 4Department of Psychiatry, University of Chicago, Chicago, Illinois. 5Department of Psychology, University of Seattle, Seattle, Washington. 6Medical Research Council, University of London, London, United Kingdom. Formerly at the 1NSERM, Centre dc Alfred Binet, Paris, France. 7Department of Psychiatry and Behavioral Science, University of Texas, Houston, Texas. 8Division TEACCH, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina. 9Address all correspondence to Alice S. Carter, Yale University, Department of Psychology, 2 Hillhouse Avenue, New Haven, Connecticut als with autism. Additional analyses within the special population normative sample address some of the limitations of employing standard and age equivalent scores from the Vineland national standardization sample with individuals with autism. Autistic individuals show a unique pattern or profile of scores across dimensions of adaptive behavior relative to age- and mental age-matched peers (Ando, Yoshimura, & Wakabayashi, 1980; Freeman, Ritvo, Yokota, Childs, & Pollard, 1988; Jacobson & Ackerman, 1990; Loveland & Kelley, 1988,1991; Rodrigue, Morgan, & Geffken, 1991; Sloan & Marcus, 1981; Volkmar et al., 1987). Studies of adaptive behavior consistently demonstrate that individuals with autism evidence significant deficits in socialization, relative strengths in daily living skills, and intermediate scores in communication (e.g., Loveland & Kelley, 1991; Volkmar et al., 1987). In addition, recent evidence suggests that children with autism show greater intradomain scatter when compared to typi /98/ / Plenum Publishing Corporation

2 288 Carter et al. cally functioning and retarded children (VanMeter, Fein, Morris, Waterhouse, & Allen, 1997). In light of the unique pattern of adaptive functioning observed in individuals with autism (cf. Carter, Gilham, Sparrow, & Volkmar, 1997), comparing individuals with autism to a similarly affected normative group rather than relying on national norms may provide a more appropriate context for understanding a particular autistic individual's current adaptive functioning. The assessment of adaptive behavior in individuals with autism has traditionally been employed along with standardized measures of intellectual functioning to determine whether or not to assign a diagnosis of mental retardation. Approximately three fourths of individuals with autism obtain verbal IQ scores in the mentally retarded range of cognitive functioning (Ritvo et al., 1989) with estimates of mental retardation among individuals with autism as high as 85% (Volkmar & Cohen, 1986, 1988). In addition to the central role of adaptive behavior in diagnosing mental retardation, the assessment of adaptive behavior is clinically informative for educational and vocational planning for individuals with autism throughout the spectrum of intellectual functioning. The traditional inclusion of adaptive behavior assessments to diagnose or rule out mental retardation contributed to the current recognition that it is important to assess adaptive skills across the spectrum of cognitive functioning within autism. To maximize the clinical utility of the assessment of adaptive behavior for individuals with autism, this paper presents new supplemental norms for individuals with autism. These norms enable clinicians and researchers to compare an individual with autism's adaptive functioning to a peer group of similarly affected individuals as well as to national normative data. Diagnosing or ruling out the presence of mental retardation is an essential component of a comprehensive evaluation for an individual with autism (Klin, Carter, & Sparrow, 1997). The most widely accepted definition of mental retardation involves the presence of subaverage cognitive functioning and deficits in adaptive behavior with onset prior to age 18 (American Psychiatric Association [APA], 1994; Grossman, 1983). Significant deficits in adaptive behavior are demonstrated by significant impairments in the performance of daily activities required for personal and social sufficiency (Sparrow, Balla, & Cicchetti, 1984) as measured by standardized instruments designed to assess adaptive behavior. Although there are state and local differences in the adoption of specific criteria for deficits in adaptive behavior, the development of instruments that provide national norms such as the Comprehensive Test of Adaptive Behavior (Adams, 1984) and Vineland Adaptive Behavior Scales (Sparrow et al., 1984) has facilitated the use of specific quantifiable guidelines. For example, to assign a diagnosis of mental retardation, some states require performance that falls approximately below the fourth percentile (e.g., Standard Score below 70-75) in two of the following adaptive behavior domains: (a) Communication, (b) Daily Living Skills/Self Help Skills, (c) Socialization/Social Functioning/Interpersonal Skills, and (d) Motor Skills. Although the assessment of mental retardation is central to a comprehensive assessment of an individual with autism (Klin et al., 1997), it is critical to recognize that individuals who are affected with both autism and mental retardation differ significantly from individuals who only meet criterion for mental retardation in the pattern of acquisition of adaptive behavior and other competencies. Indeed, significant progress has been made in the field of mental retardation by recognizing that it is not a homogeneous entity (Bailey, Phillips, & Rutter, 1996). Thus, when evaluating an individual with autism and mental retardation, the use of special population norms for mentally retarded individuals does not provide an adequate comparison group. Independent of their level of cognitive functioning, individuals with autism have a profound inability to relate to people as well as language abnormalities and stereotyped repetitive behaviors (Cohen, Paul, & Volkmar, 1986; Fein, Pennington, Markowitz, Braverman, & Waterhouse, 1986; Frith, 1989; Happe, 1994; Lord, 1993; Rutter, 1978; Sigman, 1995; Wing & Gould, 1979). Indeed, Kanner's (1943) original description of the syndrome of autism emphasized the social impairment of individuals with autism. This focus on the centrality of social deficits has continued in more recent definitions and descriptions of the clinical features of autism (Bailey et al., 1996; Cohen et al., 1986; Fein et al., 1986; Rutter, 1978; Wing & Gould, 1979). In addition, the most recent edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; APA, 1994) is consistent with Kanner's early conceptualization of autism in highlighting social deficits. Thus, the deficits observed in social functioning are far greater than what one would expect, even given the typically observed cognitive limitations. As the social and linguistic deficits and

3 Vineland Supplementary Norms for Autism 289 deviance present in autism impact on the day-to-day performance of adaptive behaviors, it is not surprising that even high-functioning individuals with autism typically show significant deficits in adaptive behaviors (cf. Carter et al., 1996). Recently, Volkmar and colleagues argued that social deficits in individuals with autism can be quantified by determining the magnitude of the discrepancy between a standard score in the adaptive domain of socialization and mental age (Volkmar, Carter, Sparrow, & Cicchetti, 1993; Gilham, Carter, Volkmar, & Sparrow, 1998). This conceptual model emphasizes developmental delay in the acquisition of adaptive social behaviors in contrast to previous categorical models that highlighted developmental social, linguistic and behavioral deviance. They demonstrated that the Vineland Adaptive Behavior Scales (Sparrow et al., 1984) were sensitive to the overall impairments observed in autism and could be used to quantify the social deficits observed among autistic individuals. VanMeter et al. (1997) examined intratest scatter among preschoolers who were carefully matched to either typically functioning or mentally deficient children on Vineland raw scores to highlight the presence of deviance as well as delay in the acquisition of adaptive behavior in autism. While these studies have implications for research in the area of autism, they also highlight the clinical utility of the assessment of adaptive behavior in autism and more specifically the use of the Vineland Adaptive Behavior Scales in the assessment of adaptive behavior in autism. Autistic individuals show a unique pattern or profile of scores across dimensions of adaptive behavior relative to age- and mental age-matched peers (Ando et al., 1980; Freeman et al., 1988; Jacobson & Ackerman, 1990: Loveland & Kelley, 1988, 1991; Rodrigue et al., 1991; Sloan & Marcus, 1981; Volkmar et al., 1987). Several studies have employed the Vineland Adaptive Behavior Scales to document this unique pattern of adaptive behavior across domains (i.e., Communication, Daily Living Skills, and Socialization) in individuals with autism as compared with individuals with mental retardation. These studies consistently indicate that while individuals with mental retardation have relatively flat profiles across adaptive behavior domains, autistic children and adults evidence significant deficits in the Socialization Domain, when compared to relative strengths in Daily Living Skills, and intermediate scores on Communication (Loveland & Kelley, 1991; Volkmar et al., 1987). A similar relative deficit in socialization is apparent when individuals with autism are matched to normally developing children on the basis of overall adaptive behavior scores (Rodrigue et al., 1991). While the pattern of a relative deficit in socialization and a relative strength in daily living skills is apparent early in life (Loveland & Kelley, 1991) and in older individuals with autism (Volkmar et al., 1987), it is important to note that adaptive behavior profiles for individuals with autism may be affected by age (Jacobson & Ackerman, 1990) and level of cognitive functioning (Burack & Volkmar, 1992). Individuals with autism with IQ scores in the average range and higher typically exhibit deficits in adaptive behavior, especially in the socialization domain, coupled with a high frequency of maladaptive behaviors (Burack & Volkmar, 1992; Freeman et al., 1988; Volkmar et al., 1987). While both high- and low-functioning individuals with autism display more scatter in their adaptive behavior profiles than chronologically- and mental aged-matched peers (Volkmar et al., 1987), low-functioning individuals with autism display greater scatter than high-functioning individuals with autism (Burack & Volkmar, 1992). Thus, the chronological and mental age of an individual with autism must be considered when interpreting the level and profile of observed adaptive behavior scores. A number of psychometric issues are relevant to the interpretation of Vineland Adaptive Behavior Scale scores for individuals with autism. Specifically, very low functioning individuals with autism may show relatively little scatter in standard scores across domains due to basal effects. Moreover, the use of age-equivalent scores to examine domain differences may be misleading due to lack of comparability in range across domains and subdomains. For example, several Vineland domains have relatively low ceilings (e.g., the highest possible age-equivalent scores in receptive communication is 7 years 10 months). For this reason, standard scores are recommended for use in clinical applications while raw scores are recommended in research applications. When employing raw scores, statistical analyses can be employed to control for chronological and/or mental age differences. The clinical management of children and adults with autism typically requires clinicians to make recommendations regarding appropriate educational services, vocational training and community-based living facilities (Freeman et al., 1991). Adaptive skills may be more predictive of vocational success and level of independence achieved than either academic

4 290 Carter et al. achievement or intellectual abilities. For example, Rumsey, Rapoport, and Sceery (1985) reported that 14 high-functioning men with relative deficits in socialization as assessed by the Vineland Socialization domain had considerable difficulty with vocational adjustment and independent living despite their relatively high IQs and academic achievement. Thus, independent of cognitive level, the assessment of adaptive behavior is a critical component of any comprehensive clinical assessment of individuals with autism (Klin et al., 1997). Specifically, the assessment of adaptive behaviors with standardized instruments: (a) is necessary to document a diagnosis of mental retardation; (b) can inform the diagnosis of autism; (c) can help to identify an individual's strengths and weaknesses for planning educational, vocational, and treatment goals; (d) can serve to monitor an individual's progress over time and across settings (Perry & Factor, 1989); and (e) may be used to document the efficacy of intervention programs. The unique profile and greater scatter evident among individuals with autism suggested the need to develop norms based on autistic samples (Volkmar et al., 1987). When making educational and vocational recommendations or when evaluating an individual's progress over time it is often useful to evaluate an individual with special needs relative to their own peer group rather than in contrast to a typically developing normative group (Sparrow et al., 1984). Successful individual intervention efforts and outcome evaluations require the specification of attainable goals. Employing the national standardization sample norms or even special population norms for mentally retarded individuals may lead to unrealistically high goals in socialization and an underestimate of potential within Daily Living Skills. This paper presents Special Supplemental norms for individuals with autism in four categories: (a) below age 10-mute; (b) ages 10 to 59-mute; (c) below age 10-at least some verbal skills; (d) ages 10 to 59-at least some verbal skills. METHOD Participants The sample included 684 autistic individuals from records of evaluations performed either as part of the DSM-IV autism/pdd field trial collaborative study (137 cases) (Volkmar et al., 1994) or from five different sites: the Yale Child Study Center Developmental Disabilities Clinic (225 cases), Division TEACCH (195 cases), University of Texas (42 cases), University of Washington (43 cases), and the Center Alfred Binet (42 cases). These 684 individuals (497 male, 157 female, 30 cases missing gender) had participated in a comprehensive evaluation that included the administration of the Vineland (survey or expanded form), psychological testing, and diagnostic assessment by highly experienced examiners. As the focus of the majority of the assessments was to document a primary diagnosis of Autism, it is possible that some individuals may have met criteria for disorders that have recently been included in the DSM- IV, including Childhood Disintegrative Disorder (Volkmar & Rutter, 1995) or Asperger syndrome. In 42% of the cases the individual was noted to be largely or entirely mute. The definition of mute, derived verbatim from the DSM-IV field trial, was as follows: "little or no language, uses language only occasionally; only single words or echolalic language with limited or no spontaneous speech." The mean age of cases was years (SD = 7.83); cases ranged from preschool to middle age (ages 2 to 59 years). Assessments of full-scale IQ based on various assessment instruments were available in 606 cases; in the remaining 78 cases the individual was noted to be "untestable." The total sample was divided into four norming groups based on age (younger than 10 years of age or 10 to 59 years of age) and language status (mute and verbal). The distinction between mute and verbal is critical for intervention and can be determined without formal psychological assessment. Although ideally, special population norms would be available for smaller chronological and mental age bands (i.e., preschool, school-aged, adolescents, adults), sample size limitations precluded the creation of more refined groups. The decision to divide the sample, at 10 years of age was based on a desire to acknowledge the different developmental concerns of younger versus older children and adults with autism as well as by pragmatic power constraints within the available sample. Table I presents sample characteristics for each of the of the four norming groups (i.e., gender, IQ, and age). The preponderance of males in each of the autistic norm groups is expected given the increased frequency of the condition in males (Lord & Schopler, 1987; Volkmar, Szatmari, & Sparrow, 1993). In addition, consistent with the increased severity in affected

5 Vineland Supplementary Norms for Autism 291 Gender Male Female Missing Age below 10 (n = 141) n % Table I. Sample Characteristics Verbal Age 10 and above (n = 186) n % Age below 10 (n = 252) n % Mute Age 10 and above (n = 104) n % Age M ±SD Range 6.20 ± ± ± ± IQ < >85 Missing females as compared to males (Volkmar et al., 1993), females were more likely to be mute, x2(1) = 4.08, p <.05, and severely delayed cognitively than males, X2(5) = 11.08,p <.05. All cases had a primary diagnosis of autism as assigned by the clinician on the basis of a comprehensive assessment. In most cases this diagnosis was also supported by the results of assessment instruments specifically developed for autism (e.g., the Children's Autism Rating Scale; Schopler, Reichler, & Renner, 1988; the Autism Behavior Checklist; Krug, Arick, & Almond, 1980; Autism Diagnostic Interview-Revised; Lord, Rutter, & Le Couteur, 1994). As both DSM-IV (APA, 1994) and ICD-10 (World Health Organization [WHO], 1992) diagnoses were under preparation at the time of the data collection, it was not always possible to utilize these most recent categorical diagnostic systems. However, for those cases provided as part of the DSM-IV autism/pdd field trial and for all of the Yale cases, the most recent ICD-10 (WHO, 1992) criteria were applied and only subjects who met the ICD-10 criteria were included in the sample. The majority of the cases were receiving special educational services but were not in residential placements. Cases did vary significantly in the distribution of age, sex, IQ, and adaptive functioning across sites. However, due to the widely discrepant numbers of cases from each site (e.g., 42 vs. 252), site was not included as a control variable in analyses. Measures Vineland Adaptive Behavior Scales-Survey Form (Sparrow et al., 1984). The Vineland Adaptive Behavior Scales evaluate children's personal and social sufficiency in a semistructured interview with a primary caregiver. This instrument assesses four areas of adaptive behavior: Communication, Daily Living Skills, Socialization, and Motor Skills. Communication refers to those skills required for receptive, expressive, and written language; Daily Living Skills includes the practical skills needed to take care of oneself and contribute to a household and community; Socialization pertains to those skills needed to get along with others, regulate emotions and behavior, as well as skills involved in leisure activities such as play; Motor Skills, comprising both fine and gross motor items, are typically assessed in individuals below the age of 6 years or when significant difficulty in motor development is suspected. The Vineland also contains a Maladaptive Behavior Domain, which assesses the presence of problematic behaviors that

6 292 Carter et al. interfere with an individual's functioning. The Maladaptive Behavior Domain is administered to children aged 5 and older and includes both behaviors that are common in early development but are less common as children get older and more serious behaviors that are of concern throughout development. Based on a nationally representative sample, reliabilities for each of four domains (Communication, Daily Living Skills, Socialization, Motor Skills) range from In some cases the Expanded Vineland was administered rather than the briefer Survey form for which the supplemental norms are derived. As all of the items on the survey form are included in the Expanded form, the Survey form was derived based on the responses to the shared items. Concurrent validity between Vineland (Sparrow et al., 1984) and the AAMD Adaptive Behavior Scale School Edition (Lambert, Windmiller, Thanringer, & Cole, 1981) is good (Perry & Factor, 1989). Statistical Analysis Percentile ranks corresponding to domain raw scores were developed separately for each of the four norming groups. Due to the lack of variability in standard score distributions for these four samples, raw score frequency distributions were used to develop the percentile rank norms. Percentile ranks for the four autism samples were developed by first determining the cumulative percentages for raw scores. Frequency distributions and the first four moments of the distributions (mean, standard deviation, skewness, and kurtosis) were obtained. An algorithm developed by Hill (1976; Hill, Hill, & Holder, 1976) and Roid (1989) that is based on systems of frequency curves described by Johnson (1949) was used to calculate the percentile ranks. This algorithm provides fitted curves that preserve the first four moments of the observed raw score distributions and yields percentile estimates that are smoothed across the distributions. This method is comparable to the method that was employed with the Vineland standardization sample for the development of national percentiles (Sparrow et al., 1984, p. 23). RESULTS Prior to presenting the special norm tables, several analyses were conducted to describe similarities Prior to presenting the special norm tables, several analyses were conducted to describe similarities and differences observed in the pattern of adaptive functioning across the four groups from which the special norms were derived: Mute and verbal individuals with autism who were below 10 years of age or 10 years of age or older. This large sample allowed the opportunity to replicate previous findings that suggested the need to develop special population norms. Moreover, as this sample was culled from several different clinics, it was important to determine whether there were age differences in the younger and older samples across mute and verbal subjects. Analysis of variance (ANOVA) revealed an age group by mute status interaction, F(l, 679) = 24.37, p <.0001, such that within the older age group, verbal individuals were significantly older than mute individuals (19.3 vs. 14.9, respectively). Given the lack of comparability across these two groups, age was included as a covariate in subsequent analyses designed to examine group differences in Vineland domain standard scores and age equivalents.10 Group Comparisons of Adaptive Behavior Scores The first set of analyses employed analysis of covariance (ANCOVA) to examine differences in Vineland domain standard scores and age equivalents across the two group factors (mute versus verbal and younger than age 10 vs. 10 years old and older) with continuous age as a covariate. Means and standard deviations for raw scores, standard scores, and age equivalents for Communication, Daily Living Skills, Socialization, and the Adaptive Behavior Composite are presented in Table II. Table III presents age-adjusted standard and age-equivalent scores for the three Vineland domains that were assessed across the two age groups for mute and verbal individuals. Standard Scores. The full model for the Communication domain standard score, which included continuous age as a covariate and main effects and the interaction of age group and mute status was statistically significant, F(4, 678) = 65.84, p < Age, F(l, 678) = 18.93, p <.0001; age group, F(1, 678) = 51.44, p <.0001; and mute status, F(1, 678) = 58.09, p <.0001, were statistically significant but the interaction term was not. Children below 10 years of age As the younger children exhibited much higher standard scores than the older groups, a decision was made to covary age for both sets of analyses. A separate set of analyses that did not include age as a covariate yielded comparable findings, than the older groups, a decision was made to covary age for both sets of analyses. A separate set of analyses that did not include age as a covariate yielded comparable findings.

7 Vineland Supplementary Norms for Autism 293 Vineland domain Table II. Standard and Age-Equivalent Scores for Vineland Domainsa Below 10 years of age (n = 141) M SD Verbal Above 10 years of age (n = 186) M SD Below 10 years of age (n = 252) M SD Mute Above 10 years of age (n = 104) M SD Communication Raw scores Standard scores Age equivalent a a a a a Daily Living Raw scores Standard scores Age equivalent b 3.20, a b b Socialization Raw scores Standard scores Age equivalent C b b 1.70, b Composite Standard scores adifferent letter subscripts indicate significant differences between domains within groups for standard scores. Different numeric subscripts indicate significant differences between domains within groups for age equivalents (p <.05). Table HI. Mean Standard and Age-Equivalent Scores for Vineland Domains Adjusted for Agea Vineland domain Below 10 years of age (n = 141) M Verbal Above 10 years of age (n = 186) M Below 10 years of age (n = 252) M Mute Above 10 years of age (n = 104) M Communication Standard scores Age equivalent 59.74a 3.70a 47.26b 2.54b 43.31b 4.76c 32.82c 2.46b Daily Living Standard scores Age equivalent 58.54a 4.59a 54.16b 4.17b 33.25c 3.83b 29.94c 3.23c Socialization Standard scores Age equivalent 59.14a 3.04a 56.73a 2.93a 35.08b 2.01b 33.57b adifferent letter subscripts indicate significant differences between cells within a domain across groups for standard scores and age equivalents (p <.05). 1.81b had higher Communication standard scores than individuals 10 years of age and older (adjusted means, combining mute and verbal subjects were and 38.06, respectively, p <.0001). Consistent with expectations, verbal individuals were more likely to have higher scores than mute individuals (adjusted means were and 40.04, respectively, p <.0001). The full model for the Daily Living Skills standard

8 294 Carter et al. score was statistically significant, F(4, 678) = 30.09, p <.0001; with age, F(1, 678) = 17.48, p <.0001; age group, F(l, 678) = , p <.0001; and mute status, F(l, 678) = 4.98, p <.05, contributing significantly to the model. The interaction term was not statistically significant. Younger individuals (i.e., younger than 10 years of age) had higher standard scores than older individuals (i.e., those 10 years of age or older) with autism (adjusted means combining mute and verbal individuals were and 31.59, respectively, p <.0001) and verbal individuals achieved higher scores than mute individuals (adjusted means, combining younger and older individuals, were and 42.05, respectively, p <.05). The full model for Socialization standard scores was also statistically significant, F(4, 678) = , p < Only age group, F(l, 678) = , p <.0001, contributed significant variance to the model. There was no effect of continuous age as a covariate, main effect of mute status, or interaction of age group and mute status. Thus, consistent with findings for Daily Living Skills, younger children (i.e., younger than 10 years of age) were more likely to have higher standard scores on Socialization than older individuals (i.e., 10 years of age or older; adjusted means, combining mute and verbal individuals, were and 34.33, respectively, p <.0001). However, in contrast to Communication and Daily Living Skills, mute and verbal individuals did not differ in Socialization. Age Equivalent Scores. The full model for the Communication age-equivalent scores was significant, F(4, 678) = 67.41, p <.0001; with age group F(l, 678) = 30.84, p <.0001; mute status, F(l, 678) = 69.42, p <.0001; and the interaction between age group and mute status, F(l, 678) = 7.51, p <.01, contributing significantly to the model. There was no main effect of continuous age as a covariate. A comparison of adjusted means across the four groups indicated that younger verbal children were least impaired, older mute individuals were most impaired, and younger mute and older verbal individuals were functioning in the midrange (see Table III for adjusted means). The full model for the Daily Living Skills age equivalent was statistically significant, F(4, 678) = , p <.0001; with age as a covariate, F(l, 678) = , p <.0001; age group, F(l, 678) = 12.57, p <.001; and mute status, F(l, 678) = 9.64, p <.01, contributing significant variance. The interaction term was not significant. Younger children appeared to be less impaired than older individuals (adjusted means were 4.37 and 3.53, respectively, p <.001) and verbal individuals were less impaired than mute individuals (adjusted means were 4.21 and 3.70, respectively, p <.01). For the Socialization age equivalent score, the full model was significant, F(4, 678) = 53.74, p <.0001; with age as a covariate, F(l, 678) = , p <.0001; and age group, F(l, 678) = 22.72, p <.0001, contributing significantly. Neither mute status or the interaction term contributed significant variance. Consistent with the Communication and Daily Living Skills domains, younger children appeared less impaired than older individuals (adjusted means, combining mute and verbal individuals were 2.99 and 1.91, respectively, p <.001). Profile Analyses To examine similarities and differences in the profiles of domain scores across the four groups, two repeated measures ANOVAs were conducted to compare standard scores and age equivalents scores across the three Vineland domains assessed at all ages (i.e., Communication, Socialization, and Daily Living Skills). As the critical comparison was within group, age was not covaried for this analysis. Parallel analyses that included age as a covariate provide the same pattern of results. Specifically, a model was tested that included main effects of mute status (mute vs. verbal) and age group (below age 10 years vs. age 10 or older) and Vineland domain standard scores and age equivalents as a repeated factor. The expectation was that there would be a main effect of the repeated Vineland profile factor such that all individuals with autism would show highest scores in Daily Living Skills and poorest performance in Socialization. There was also an expectation that due to basal effects for the older mute group, there would be an interaction between mute status, age group and Vineland profile. Standard Score Profiles. Results for the three domain standard scores revealed a main effect for Vineland profile (Wilks's X =.9877), F(2, 678) = 4.22, p <.05; an interaction between Vineland profile and age group (Wilks's X =.9371), F(2, 678) = 22.74, p <.0001; an interaction between Vineland profile and mute status (Wilks's K =.9187), F(2, 678) = 30.02, p <.0001); and a trend for a three-way interaction between Vineland profile, age group, and mute status (Wilks's X =.9929), F(2, 678) = 2.42, p <.10. Both age grouping and mute status contrib-

9 Vineland Supplementary Norms for Autism 295 uted significant variance to differences between each possible pairing of domains (i.e., Communication vs. Socialization, Communication vs. Daily Living Skills, and Socialization vs. Daily Living Skills; all ps <.001). The interaction term was only statistically significant in predicting to differences between Communication and Daily Living Skills (F = 4.82, p <.05). Age-Equivalent Profiles. For the age-equivalent scores, there was a main effect for Vineland profile (Wilks's A. =.4336), F(2, 678) = , p <.0001; an interaction between Vineland profile and age group (Wilks's X =.7481), F(2, 678) = , p <.0001; an interaction between Vineland profile and mute status (Wilks's X =.8711), F(2, 678) = 50.12, p <.0001; and a significant three-way interaction between Vineland profile, age group, and mute status (Wilks's A =.98427), F(2, 678) = 5.42, p <.01. Both age grouping and mute status contributed significant variance to differences between each possible pairing of domains (i.e., Communication vs. Socialization, Communication vs. Daily Living Skills, and Socialization vs. Daily Living Skills; all ps <.001). In addition, the interaction term was statistically significant in predicting differences between Communication and Socialization (F = 5.31, p <.05) and Daily Living Skills and Socialization (F = 6.65, p <.05) but not for differences in Communication and Daily Living Skills. Although each of the four groups (i.e., younger and older mute and verbal individuals) evidenced a statistically significant profile effect for both standard scores and age-equivalent scores, patterns of differences across standard patterns of differences across standard scores and age equivalents were not comparable. Most groups evidenced the expected pattern of a relative strength in Daily Living Skills and a relative weakness in Socialization when profiles of ageequivalent scores were examined. In contrast, standard scores revealed inconsistent and unexpected patterns across the four groups (see Table II that details significant differences in means across domains within each group). For example, the younger mute group exhibited a relative strength on Daily Living Skills on the age-equivalent scores but evidenced a relative strength in Socialization when standard scores were examined. With respect to the supplementary norms, percentile ranks are reported in Tables IV through X. Table IV. Supplemental Norm Group Percentile Ranks Corresponding Raw Scores: Ages Less Than 10 Years Old Autism Special Population: Mute Supplementary norm group percentile rank Communication Daily Living Skills Raw scores Socialization Motor Skills SP 99 SP 98 SP 95 SP 90 SP 85 SP 80 SP 75 SP 70 SP 65 SP 60 SP 55 SP 50 SP 45 SP 40 SP 35 SP 30 SP 25 SP 20 SP 15 SP 10 SP 5 SP 2 SP

10 296 Carter et al. Table V. Supplemental Norm Group Percentile Ranks Corresponding Raw Scores: Ages Less Than 10 Years Old Autism Special Population: Verbal Supplementary norm group percentile rank Communication Daily Living Skills Raw scores Socialization Motor Skills SP 99 SP 98 SP 95 SP 90 SP 85 SP 80 SP 75 SP 70 SP 65 SP 60 SP 55 SP 50 SP 45 SP 40 SP 35 SP 30 SP 25 SP 20 SP 15 SP 10 SP 5 SP 2 SP Table VI. Supplemental Norm Group Percentile Ranks Corresponding Raw Scores: Ages 10 Years and Older Autism Special Population: Mute Supplementary norm group percentile rank Communication Raw scores Daily Living Skills Socialization SP 99 SP 98 SP 95 SP 90 SP 85 SP 80 SP 75 SP 70 SP 65 SP 60 SP 55 SP 50 SP 45 SP 40 SP 35 SP 30 SP 25 SP 20 SP 15 SP 10 SP 5 SP 2 SP

11 Vineland Supplementary Norms for Autism 297 Table VII. Supplemental Norm Group Percentile Ranks Corresponding Raw Scores: Ages 10 Years and Older Autism Special Population: Verbal Supplementary norm group percentile rank SP 99 SP 98 SP 95 SP 90 SP 85 SP 80 SP 75 SP 70 SP 65 SP 60 SP 55 SP 50 SP 45 SP 40 SP 35 SP 30 SP 25 SP 20 SP 15 SP 10 SP 5 SP 2 SP 1 Communication Raw scores Daily Living Skills Socialization Table VIII. Supplemental Norm Group Percentile Ranks Corresponding to Sum of Raw Scores: Ages Less Than 10 Years Old Autism Special Population: Mute Supplementary norm group percentile rank Sum of 3 domain raw scores (Communication + Daily Living Skills + Socialization) Sum of 4 domain raw scores (Communication + Daily Living Skills + Socialization + Motor) Up ~Up

12 298 Carter et at. Table IX. Supplemental Norm Group Percentile Ranks Corresponding to Sum of Raw Scores: Ages Less Than 10 Years Old Autism Special Population: Not Mute Supplementary norm group percentile rank Sum of 3 domain raw scores (Communication + Daily Living Skills + Socialization) Sum of 4 domain raw scores (Communication + Daily Living Skills + Socialization + Motor) Up ~Up Table X. Supplemental Norm Group Percentile Ranks Corresponding to Sum of Raw Scores Ages Greater Than or Equal to 10 Years Old: Autism Special Population Sample Supplementary norm group percentile rank Sum of 3 domain raw scores (Communication + Daily Living Skills + Socialization) Not mute (n = 171) Mute (n = 98) ~Up Up

13 Vineland Supplementary Norms for Autism 299 Tables IV and V present the supplementary norm group percentile ranks corresponding to raw scores in mute and verbal children with autism less than 10 years old across the four domains assessed by the Vineland Adaptive Behavior Scales. Tables VI and VII present the supplementary norm group percentile ranks corresponding to raw scores in mute and verbal individuals with autism who are 10 years of age or older across three domains assessed by the Vineland Adaptive Behavior Scales. The motor domain was not included in the older samples. Finally, Tables VIII, IX, and X present supplementary norm group percentile ranks corresponding to the sums of raw scores across three or four domains for mute and verbal younger and older samples. DISCUSSION This paper presents special population norms for four groups of individuals with autism: (a) mute children under age 10 years; (b) children with at least some verbal skills under age 10 (verbal); (c) mute individuals who are age 10 or older; and (d) verbal individuals who are age 10 or older. The sample was ascertained from cases referred for the DSM-IV autism/pdd field trial collaborative study and five other university-based sites with expertise in the diagnosis of autism. Thus, although the sample is one of "convenience," the cases that were utilized to generate these special population norms most likely represent valid cases of autism that are representative of the general population of individuals with autism. Representativeness has been increased by aggregating individuals across sites that tend to serve slightly different populations of individuals with autism. That the total sample included the expected higher ratio of males to females and of mute females relative to mute males (Volkmar et al., 1993) lends further support to the likelihood that the sample is representative. In addition, it should be noted that the age range of the older samples is from years for mute and years for verbal individuals, with 95% of the verbal individuals younger than age 35 years at the time of assessment. Thus, the use of these norms is most appropriate for individuals with autism below age 35 years. Differences in cognitive functioning across the four groups (e.g., the younger verbal group achieved the highest IQ scores), although statistically significant should not interfere with the clinical use of the special population norms across functional levels in each of the four groupings. The observed pattern of verbal individuals achieving higher cognitive and adaptive scores than mute individuals is not surprising. Previous research would suggest that individuals with autism at all levels of cognitive functioning would exhibit a distinctive adaptive profile (Ando et al., 1980; Freeman et al., 1988; Jacobson & Ackerman, 1990: Loveland & Kelley, 1988, 1991; Rodrigue et al., 1991; Sloan & Marcus, 1981; Volkmar et al., 1987). Of course, when developing special population norms an epidemiological sample of individuals with autism would ultimately be preferable to aggregating across clinical sites. Consistent with previous research, individuals with autism demonstrated a unique profile of adaptive behavior scores across the domains of the Vineland Adaptive Behavior Composite. Specifically, when age equivalent scores were employed in profile analyses, there was a relative strength in Daily Living Skills, a relative weakness in Socialization, and intermediate scores on Communication. In contrast, profile analyses employing standard scores were not consistent with expectations based on previous research. The inconsistency in these findings is a reflection, in part, of range restriction due to basal effects in this population. The fact that typically employed standard scores revealed inconsistent patterns highlights the need for the special population norms presented in this paper. When examining adaptive behavior profiles, the use of age-equivalent scores appear more appropriate for lower functioning and/or mute individuals, as basal effects are most likely to obscure actual differences between adaptive domains. Scores for the younger and older mute individuals were significantly lower than for the individuals with some verbal skills, suggesting the need for developing independent norms for these two groups. Younger children's higher standard scores may in part reflect a developmental feature of the disorder, such that the failure to acquire appropriate adaptive skills contributes to a greater relative deficit with age. This could be part of a more global developmental decline in functioning, as younger verbal children achieved the highest IQ scores. However, it is likely that floor effects are responsible for the observed patterns. The basal standard scores for younger children are often higher than for older individuals; the lowest standard score possible at a very young age may be 40, whereas for the older individuals the lowest possible standard score is 20. It is important to note that this problem is not unique to the Vineland

14 300 Carter et al. Adaptive Behavior Scales. Indeed, the Vineland was the first standardized instrument of adaptive behavior to develop a normative range that included standard scores as low as 20. Moreover, the availability of special supplementary norms for individuals with autism addresses this psychometric problem in the Vineland, especially for younger children. Dividing the sample on the basis of mute status (i.e., mute vs. at least some verbal skills) rather than relying on mental age or IQ scores, greatly simplifies the employment of these special population norms and extends the norms to individuals who may be labeled "untestable." Given the importance of including an assessment of adaptive behavior skills for educational and vocational planning for individuals with autism and the difficulty inherent in obtaining an adequate assessment of IQ (cf. Klin et al., 1997), classification that is independent of a determination of IQ is advantageous. The assessment of adaptive behavior in individuals with autism is central to a comprehensive, developmentally sensitive assessment. As noted earlier, including standardized assessments of adaptive behavior: (a) is necessary for documenting mental retardation, a condition that is extremely common among individuals with autism; (b) can help identity strengths and weaknesses when planning educational, vocational, residential, or home-based treatment goals; and (c) can serve to monitor progress over time and across settings. In addition, the inclusion of adaptive behavior can provide important information for diagnosing autism. Specifically, individuals with autism achieve Socialization scores that are much lower than would be expected on the basis of their mental age (Gilham et al., 1998; Volkmar et al., 1993). Finally, the assessment of adaptive behavior can be used as an outcome measure to document the efficacy of intervention programs. The availability of special population norms for individuals with autism provides an additional point of comparison that will often be more appropriate than either national norms for typically developing individuals or special population norms for individuals with mental retardation. In contrast to individuals with mental retardation, who typically achieve a relatively flat profile of scores across adaptive behavior domains, individuals with autism show significant scatter within and across domains. Thus, an evaluation will be able to determine an individual with autism's percentile relative to national norms, which may be essential for documenting mental retardation, but will also be able to provide more realistic expectations for adaptive behavior skill acquisition based on the distribution of performance within a more comparable sample of individuals with autism. The special population norms provided in this paper can assist clinicians in assigning appropriate goals for intervention. Specifically, expectations for adaptive functioning that are based on the special populations norms will factor not only cognitive or linguistic functioning, but also the social delays and deficits that are a core feature of autism. A highfunctioning 12-year 6-month-old child with autism achieves a Verbal IQ of 95, a Performance IQ of 112, a Vineland Communication raw score of 112, which corresponds to a Standard Score of 68 (2nd percentile), a Daily Living Skills raw score of 138, which corresponds to a Standard Score of 76 (5th percentile), and a Socialization raw score of 52, which corresponds to a Standard Score of 40 (below 0.1 percentile). As this child is not mentally retarded, no previously available special population norms would be appropriate. The raw scores that correspond to these standard scores were obtained in Appendix C Table B.1 of the Vineland manual (Sparrow et al., 1984, p. 213). Using the special population autism norms presented in Table VII for individuals 10 years and older who are not mute, the child's raw scores correspond to the following percentile scores: SP 75 in Communication, SP 80 in Daily Living Skills, and SP 45 in Socialization. Thus, Socialization appears to be a relative weakness and a potential focus for intervention even when employing the special population norms. A second 12-year 6-month-old boy with minimal verbal expression is declared untestable, but achieves the following Vineland standard scores based on parent report: a Vineland Communication raw score of 73, which corresponds to a Standard Score of 35 (below 0.1 percentile), Daily Living Skills raw score of 101, which corresponds to a Standard Score of 37 (0.1 percentile), and a Socialization raw score of 47, which corresponds to a Standard Score of 36 (below 0.1 percentile). The new special population norms yield the following profile: SP 75 in Communication, SP 75 in Daily Living Skills, and SP 65 in Socialization. In this case, the profile of scores does not shift, but expectations for performance can be modified appropriately. In contrast to intellectual functioning, adaptive behavior is modifiable. For all individuals, however, cognitive functioning will set some constraints on the level of adaptive functioning that can be achieved.

15 Vineland Supplementary Norms for Autism 301 Specifically, it is not reasonable to expect an individual to achieve a level of adaptive functioning that is significantly more advanced than their intellectual level or mental age. For individuals with autism, social deviance sets further constraints, especially within the Socialization domain. As the acquisition of specific adaptive behavior skills is often a key component of intervention for individuals with autism, it is critical that individuals designing such intervention programs set attainable goals across domains of adaptive functioning. When such goals are met, clients, staff, and family members experience increased self-efficacy. 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