Characteristics of adults with autism sp (2)

Research in Autism Spectrum Disorders 6 (2012) 741–751

Contents lists available at SciVerse ScienceDirect

Research in Autism Spectrum Disorders
Journal homepage: http://ees.elsevier.com/RASD/default.asp

Characteristics of adults with autism spectrum disorder who use adult
developmental disability services: Results from 25 US states
Amy S. Hewitt a,*, Roger J. Stancliffe b, Annie Johnson Sirek a, Jennifer Hall-Lande a, Sarah Taub c,
Joshua Engler c, Julie Bershadsky c, Jon Fortune c, Charles R. Moseley d
a

Research and Training Center on Community Living, University of Minnesota, 102 Pattee Hall, 150 Pillsbury Drive SE, Minneapolis, MN 55455, USA
University of Sydney, Faculty of Health Sciences, Rm 119, J Block, 75 East Street, PO Box 170, Lidcombe, NSW 1825 Australia
Human Services Research Institute, 2336 Massachusetts Avenue, Cambridge, MA 02140, USA
d
National Association of State Directors of Developmental Disabilities Services, 113 Oronoco Street, Alexandria, VA 22314, USA
b
c

A R T I C L E I N F O

A B S T R A C T

Article history:
Received 17 June 2011
Received in revised form 19 October 2011
Accepted 19 October 2011

There is a significant increase in the prevalence of autism and autism spectrum disorders
(ASD) in children with estimates now reaching 1 in 110 children in the United States.
Families report difficulties in finding services for their young and adult children. Many
adults with ASD receive services and supports through state intellectual and
developmental disabilities (IDD) adult service systems. This study presents descriptive
data on a random sample of 12,382 individual users of adult IDD services from 25 states
that included 1002 individuals with an autism diagnosis (8.1%). Data are provided on
demographic characteristics, diagnoses, communication and relationship status for
adults with autism/ASD and a comparison of these findings for IDD service users who
have other diagnoses.
ß 2011 Elsevier Ltd. All rights reserved.

Keywords:
Intellectual disabilities
Autism spectrum disorder

1. Introduction
1.1. Background
The term ‘‘autism spectrum disorders’’ encompasses a range of behaviorally defined conditions that include: autistic
disorder (autism), Asperger disorder, and pervasive developmental disorder—not otherwise specified (PDD-NOS). Autism
spectrum disorder (ASD) is characterized by qualitative impairments in communication and social interaction, as well as
restricted, repetitive and stereotyped patterns of behavior (American Psychiatric Association (APA), 2000).
Many individuals with ASD also experience other developmental disabilities, including intellectual disabilities (ID).
Recent estimates of the presence of co-occurring ID among children with ASD range from 19.2% (Boulet, Boyle, & Schieve,
2009) to 41% (Centers for Disease Control and Prevention (CDC), 2009). In the past, when ASD was thought of solely in terms
of autistic disorder (excluding other ASDs), co-occurring ID was identified in two-thirds or more of children with ASD (Rutter,
2005). In other words, even without eligibility for services arising specifically from their ASD, those individuals with ASD and
ID likely were eligible for intellectual and developmental disabilities (IDD) services on the basis of their ID alone. Thus with

Abbreviations: HCBS, Home and Community Based Services; ICF/MR, Intermediate Care Facilities for the Mentally Retarded; NCI, National Core
Indicators.

* Corresponding author. Tel.: +1 612 625 1098; fax: +1 612 625 6619.
E-mail addresses: hewit005@umn.edu (A.S. Hewitt), roger.stancliffe@sydney.edu.au (R.J. Stancliffe), joh02055@umn.edu (A. Johnson Sirek),
hall0440@umn.edu (J. Hall-Lande), staub@hsri.org (S. Taub), jenger@hsri.org (J. Engler), jbershadsky@hsri.org (J. Bershadsky), jfortune@hsri.org (J. Fortune),
cmoseley@nasddds.org (C.R. Moseley).
1750-9467/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.rasd.2011.10.007

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the rising prevalence of ASD and the introduction of policy initiatives in a number of states intended to provide access to IDD
services on the basis of ASD diagnosis alone, there is likely an increasing number of IDD service users with ASD.
Quality of life among adults with ASD is related to receipt of formal supports that are individualized and comprehensive
(Renty & Roeyers, 2006). Most individuals with ASD experience poor adult outcomes (Billstedt, Gillberg, & Gillberg, 2005;
Howlin, Goode, Hutton, & Rutter, 2004) with ongoing challenges of communication, social relationships, social interactions,
employment, and independence (Howlin, Mawhood, & Rutter, 2000; Lawer, Brusilovskiy, Salzer, & Mandell, 2009).
Thus, the research and service context for adults with ASD includes indicators of lowered quality of life and issues of
access to adequate service and support systems. State IDD adult service systems represent one major source of services and
support, but little is known about the number of adults (age 18 years or older) with ASD who use these services, the types of

services they use, and the characteristics of adult IDD service users with ASD as compared to other IDD service users who are
not so diagnosed. The current study draws on a 25-state cross-sectional sample of adults from the National Core Indicators
(NCI) program to provide descriptive information about these issues.
1.2. Prevalence of ASD and access to adult IDD services
Diagnostic criteria that incorporated a spectrum of autistic symptoms were implemented in the early 1990s. Rates of
ASD diagnoses have been increasing steadily since 1990 (Newschaffer, Falb, & Gurney, 2005). For example, a 57% increase in
prevalence was observed among eight-year-olds from 2002 to 2006 (CDC, 2009), and one in 110 children in the United
States are currently diagnosed with ASD (CDC, 2010). These statistics point to a vast and rapidly increasing demand for
effective systems that support individuals with ASD throughout the lifespan. However, with the trend toward early
diagnosis of ASD, it is likely that 10–15 years will elapse before these recently documented increases in ASD prevalence will
in turn affect service user numbers in the adult IDD system to a similar degree. In recent years policy initiatives within
several state IDD service systems have expanded access to persons with ASD diagnoses by amending current service
eligibility criteria to include ‘‘related conditions’’ clauses that allow access by persons with ASD diagnoses or by the
development of separate autism-specific Home and Community Based Services (HCBS) Section 1915(c) Medicaid waiver
programs.
There has been limited and conflicting evidence regarding the prevalence of adults diagnosed with ASD (Hall-Lande,
Hewitt, & Moseley, 2011). Such information has been difficult to measure reliably because, (a) lack of access to support
services often leaves adults with ASD underrepresented in the literature and underserved in their communities, and (b)
many older adults currently served in the IDD system have a primary diagnosis of developmental disabilities (DD) and may
not necessarily have an autism diagnosis even though they present with the symptoms. It is also likely that there is also a vast

cohort of adults with ASD who are not receiving needed services (Graetz, 2010). In addition, many individuals are deemed
ineligible for IDD services because their IQ scores exceed the maximum allowable for ID diagnosis or due to failure to
demonstrate functional limitations in three or more life skills (Hall-Lande et al., 2011).
1.3. Demographic characteristics of people with ASD
Boys are nearly four to five times more likely to be diagnosed with ASD than girls (Croen, Grether, & Selvin, 2002; Giarelli
et al., 2010; Kogan et al., 2009; Yeargin-Allsopp et al., 2003). Centers for Disease Control and Prevention (2009) reported that,
when ASD diagnostic estimates are stratified by gender, approximately one in 70 boys is diagnosed with ASD, while only one
in 315 girls is diagnosed with ASD. The Interactive Autism Network (IAN) (2009) proposed that the widely accepted male:
female ratio of ‘‘four or five to one’’ applies only to children with ASD and no ID. Male:female ratios of children with ASD and
ID may be closer to two to one. While fewer females are diagnosed with ASD, the severity with which females experience ASD
and co-occurring disorders is substantial. Females with ASD are more likely than males to also be diagnosed with cognitive
impairment, seizures, and epilepsy (IAN, 2009).
Inconsistency exists in the results of studies that measure variables of race and the incidence of ASD diagnoses.
Yeargin-Allsopp et al. (2003) found comparable ASD prevalence rates by race, whereas Kogan et al. (2009) reported that
black and multiracial children may have lower odds of being diagnosed with ASD than non-Hispanic white children. Other
studies have reported higher risks of ASD diagnoses among children born to black mothers (Croen et al., 2002; Keen, Reid,
& Arone, 2010).
Adults with ASD have been described as having poor social relationships and few close friends (Howlin et al., 2004). From
a sample of 42 adults with high-functioning autism or Asperger disorder, it was reported that none were married or had
children, and only a few had some kind of partner (Engstrom, Ekstrom, & Emilsson, 2003). Only a small proportion of

individuals with ASD develop intimate relationships in adolescence and adulthood (LeBlanc, Riley, & Goldsmith, 2008).
1.4. Communication issues for people with ASD
Language and social skills deficits are core characteristics of ASD. Approximately 40% of children with ASD do not talk
(CDC, 2010). Adult outcomes have been positively correlated with speech patterns at six years of age (Billstedt et al., 2005).
Symptoms of social impairment among individuals with ASD persist into adulthood and remain a distinct and ongoing
challenge (Howlin et al., 2004; Wilkins & Matson, 2009).

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1.5. Service and support use
Research on adults with ASD served within the IDD system has shown that they generally received the same types of
services as those received by persons without ASD (Human Services Research Institute (HSRI), 2008). The majority of states
in the U.S. operate HCBS Section 1915(c) Medicaid waiver programs with related conditions or related disability clauses
(Hall-Lande et al., 2011). These policies allow individuals with ASD to be eligible for HCBS that are available to people with
DD or ID. At the time of the study 11 states had designed and implemented a subset of waiver programs specifically geared
for children with ASD (CO, IN, KS, MD, MA, MO, MT, NE, NY, SC, and WI) (Hall-Lande et al., 2011). Yet, at the time of the study
only two states have implemented specific waiver programs for adults with ASD (IN and PA). Funding limitations and long
waitlists perpetuate barriers in accessing related disability services.

1.6. Study purpose
This study provides an overview of the characteristics of individuals with an autism/ASD diagnosis included within a
random sample of IDD service recipients within 25 states. The primary research question is: What are the characteristics of
adults with ASD who receive HCBS and Intermediate Care Facilities for the Mentally Retarded (ICF/MR) services in the United
States? How are these characteristics similar or different from service recipients without an ASD diagnosis?
2. Method
2.1. Sample
2.1.1. State selection
Data came from 25 of the 26 states that participated in the NCI program in 2006–2007 and 2007–2008. The exception,
Maine (N = 436), did not provide data about autism/ASD diagnosis. The 25 states that took part in this study consisted of 23
states participating in the 2007–2008 National Core Indicators (NCI) program, and two additional states that participated in
2006–2007, but not 2007–2008. The two states that provided 2006–2007 survey data were CA (Orange County only) and
WA; whereas 2007–2008 data were used for the following 23 states: AL, AR, AZ, CT, DE, GA, HI, IN, KY, LA, MO, NC, NJ, NM, NY,
OK, PA, RI, SC, TX, VT, WV, and WY.
The NCI survey is a component of a national project on quality assurance/enhancement coordinated by the Human
Services Research Institute and the National Association of State Directors of Developmental Disabilities Services. The NCI
survey is administered only in states that opt to participate in the NCI program. The participating states included in this study
are those that collected NCI Consumer Survey data (described subsequently) in 2006–2008.
2.1.2. Within state sample selection
State samples were randomly selected within each state’s population of adults (age 18 years or older) with IDD receiving

institutional, community or home-based services, or some subset of these (e.g., some states restricted their sample to
recipients of HCBS). Overall sample sizes in participating states ranged from 137 to 1594 and averaged 507. This variation in
sample size is attributed partly to the size of the population and the service systems within each of these states.
2.1.3. Participants
The total NCI participant sample consisted of 13,169 individual users of adult IDD services from 25 states, but 787 (6.0%)
had missing data on the presence of an autism/ASD diagnosis. The overall sample of 12,382 was made up of 6862 (55.6%)
men and 5485 (44.4%) women (gender missing for 35 participants), with an average age of 42.65 years (range 18–100). More
detailed information about age, gender, race, diagnoses, level of ID, marital status, and communication trends are presented
in the results section.
2.2. Instrument
Data were collected using the NCI Consumer Survey 2006–2007 version (2 states) and 2007–2008 version (24 states). This
paper draws only on data from the NCI ‘‘Background section’’ which was identical for both NCI versions. The NCI Background
section requests data on the service user’s personal characteristics, functioning, diagnoses, health, problem behavior, living
arrangements, and services. These data are obtained from individual records, setting administrators or case managers, direct
support providers, and occasionally the family members or individuals themselves. The presence or absence of an autism/
ASD diagnosis was determined by a review of the individuals’ records or state computer database and completed during the
pre-survey process. The information related to diagnoses is provided by the service coordinator/case manager and verified
by the individual or family member. The person(s) completing the diagnostic assessment and the instruments used by these
clinicians are not known. However, to be eligible for developmental disability services in all states a medical diagnosis is
required.

In this study the term ‘‘autism/ASD’’ is used to communicate results based on ASD diagnosis, because the NCI Consumer
survey versions applied in this study used the general term of ‘‘autism’’ within the survey protocol. In order to confirm

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diagnoses found in review of individuals’ records, interviewers asked respondents about disabilities other than Mental
Retardation that were noted in an individual’s records, and ‘‘autism’’ was listed as a response option. This option was updated
to ‘‘Autism Spectrum Disorder (e.g., Autism, Asperger Syndrome, Pervasive Developmental Disorder)’’ in the 2008–2009
Consumer survey instrument.
2.2.1. Interviewer training
To ensure that all interviewers received consistent training, the NCI Consumer Survey protocol is supported by a training
program for interviewers, including training manuals, presentation slides, training videos, scripts for scheduling interviews,
lists of frequently asked questions, picture response formats and a review of the survey tool.
2.2.2. Reliability
Multiple tests yielded inter-rater agreement of 92–93%, and a single examination of test-retest reliability resulted in 80%
agreement (Smith & Ashbaugh, 2001).
3. Results
3.1. Percentage of service users with autism/ASD

The sample of 12,382 participants included 1002 individuals with an autism/ASD diagnosis (8.1%, 99% CI = 7.5–8.7%).
Within the individual state samples, the percentage of sample members with autism/ASD ranged from 3.7% (99% CI = 1.3–
6.2%) to 27.4% (99% CI = 20.6–34.3%). The large variability between states led us to examine the eligibility requirements for
IDD services in the participating states to document whether these requirements were associated with systematic
differences in the percentage of service users with autism/ASD. Nineteen of the 25 states covered in this study include
‘‘related conditions’’ in their eligibility criteria for publicly funded services (Hall-Lande et al., 2011). A related condition
clause means that people with autism/ASD as well as other specified conditions are specifically identified by disability
category as eligible for the state’s developmental disability services provided they meet functional skill and IQ limitations.
Five of the states (IN, MO, NY, PA and SC) in this study also have autism-specific HCBS which means that in order to be eligible
for these services the person has to have a diagnosis of autism/ASD and have functional skill limitations (Hall-Lande et al.,
2011). Additionally, 6 states (AL, CT, HI, KY, OK and TX) had neither a related conditions clause nor an autism-specific waiver
(Hall-Lande et al., 2011).
An analysis of the differences in prevalence between states grouped according to the presence or absence of these policies
was conducted. This analysis showed that six states with neither related conditions eligibility nor targeted HCBS waiver
programs had the lowest percentage of individuals with autism/ASD (6.6%) among their aggregated samples of adult service
users, whereas the five states with both a related conditions clause and an autism-specific waiver had the highest percentage
of service users with autism/ASD (9.3%). Overall these differences were significant, x2 = 17.39, df = 2, n = 12,382, p < .001.
3.2. Analyses and significance level
Marked differences were found between participants with and without autism/ASD in terms of age, gender and level of
intellectual disability. These factors can be strongly related to other characteristics (e.g., age and level of ID are related to the

prevalence of other disabilities), and therefore it was important to control for these factors when comparing participants
with and without autism/ASD. As a result, we conducted an examination of the relationship between autism/ASD and a
number of other characteristics both as raw (univariate) comparisons and by using multivariate analysis (logistic
regression), controlling for age, gender and level of intellectual disability. Finally, given the large sample size and the number
of comparisons, an alpha was set as p < .001 for univariate analyses and p < .01 for multivariate analyses.
3.3. Demographic characteristics
3.3.1. Age
Sample members with a diagnosis of autism/ASD (M = 34.11 years, SD = 12.05) were significantly younger than other
sample members (M = 43.40 years, SD = 14.29), t (1257.2) = 22.97, p < .001 (two-tailed). As this difference was substantial
(9.3 years), we conducted a closer investigation of the age distribution of the group with autism/ASD. These data are shown
in Fig. 1. One important reason for the difference in mean age between the groups with and without an autism/ASD diagnosis
was that there was a strong overrepresentation of people with autism/ASD in the youngest age group (18–29 years) and a
notably fewer in the older age groups, x2 (4) = 404.79, N = 12,343, p < .001. It is also notable in Fig. 1 that a much larger
percentage of people with autism/ASD age 18–29 years do not have ID (2.53% of all participants in this age group or 15.32% of
individuals with autism/ASD age 18–29 years).
3.3.2. Gender
There was a substantial overrepresentation of males with an autism/ASD diagnosis, x2 (1) = 182.58, N = 12,347, p < .001.
The percentage of the overall sample males with this diagnosis (11.0%) was 2.5 times as high as the percentage of females

A.S. Hewitt et al. / Research in Autism Spectrum Disorders 6 (2012) 741–751

745

Fig. 1. Percentage of all participants in each age group with an autism/ASD diagnosis by presence of intellectual disability (ID) diagnosis.

(4.0%). Given the higher proportion of males in the sample as a whole (55.6%), the absolute numbers of males with an autism/
ASD diagnosis (n = 758) versus females (n = 240) yielded an average gender ratio of 3.16:1.
Taking this analysis further and looking at both age group and sex yields the following strong association between age and
autism/ASD diagnosis for males, x2 (4) = 291.72, N = 6843, p < .001, and for females, x2 (6) = 98.24, N = 5468, p < .001 (see
Fig. 2). Fig. 2 shows the male participants with autism/ASD as a percentage of all males within each age group, and these
same percentages for females.
Table 1 shows the numbers of males and females by age group. Both Fig. 2 and Table 1 reveal a very strong age effect,
which is much more pronounced in males than females. The male:female gender ratios for participants with autism/ASD for
each age group ranged from 3.38 to 2.63 to 1, whereas among those without an autism/ASD diagnosis the gender ratio was
much lower and ranged from 1.21 to 1.14.
3.3.3. Race
A total of 242 sample members with a diagnosis of autism/ASD were non-white (3 responded ‘‘don’t know’’). There was
no significant difference in the prevalence of autism/ASD by race, x2 (7) = 10.38, N = 12,248, p = .17 (see Table 2).
3.3.4. Hispanic/Latino status
Within the group of sample members diagnosed with autism/ASD, 62 were identified as Spanish, Hispanic or Latino and
10 selected ‘‘don’t know.’’ There was no significant difference in the prevalence of autism/ASD by ethnicity (Latino status), x2
(2) = 5.46, N = 12,120, p = .065.
3.3.5. Level of intellectual disability
Of the sample members labeled with a diagnosis of autism/ASD, 97 had no intellectual disability (ID) label, 190 had mild
ID, 255 Moderate ID, 213 Severe ID and 198 profound ID. There was an interesting bi-modal distribution of autism/ASD
diagnosis by level of intellectual disability with higher proportions for people with no ID diagnosis or severe/profound ID.

25%
Male
Female

Percentage of Participants

21.6%

20%

15%
11.7%

10%

9.3%
8.2%
6.2%
4.3%

5%

3.7%
2.3%

2.5%
1.1%

0%
18-29

30-39

40-49

50-59

60+

Age Group

Fig. 2. Percentage of all participants in each age group with an autism/ASD diagnosis by gender.

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A.S. Hewitt et al. / Research in Autism Spectrum Disorders 6 (2012) 741–751

Table 1
Number and percentage of participants by autism/ASD diagnosis, gender and age group.
Age group

Male

Female
Autism

Autism

18–29
n
%
30–39
n
%
40–49
n
%
50–59
n
%
60+
n
%
Total
n
%

Gender ratio
Autism

No

Yes

Total

No

Yes

Total

No

Yes

1265
78.4

349
21.6

1614
100.0

1040
90.7

107
9.3

1147
100.0

1.21

3.26

1281
88.3

169
11.7

1450
100.0

1103
95.7

50
4.3

1153
100.0

1.16

3.38

1507
91.8

134
8.2

1641
100.0

1275
96.3

49
3.7

1324
100.0

1.18

2.73

1218
93.8

81
6.2

1299
100.0

1091
97.7

26
2.3

1117
100.0

1.12

3.11

818
97.5

21
2.5

839
100.0

719
98.9

8
1.1

727
100.0

1.14

2.63

6089
89.0

754
11.0

6843
100.0

5228
95.6

240
4.4

5468
100.0

1.16

3.16

Table 2
Number and percentage of participants with and without an autism/ASD diagnosis by race.
Race

American Indian or Alaska native
Asian
Black or African American
Pacific Islander
White
Other race not listed
Two or more races
Don’t know
Total

Autism diagnosis
No

Yes

Total

147
1.3%
283
2.5%
1764
15.7%
68
0.6%
8047
71.5%
795
7.1%
103
0.9%
47
0.4%
11,254
100.0%

7
0.7%
25
2.5%
138
13.9%
8
0.8%
749
75.4%
55
5.5%
9
0.9%
3
0.3%
994
100.0%

154
1.3%
308
2.5%
1902
15.5%
76
0.6%
8796
71.8%
850
6.9%
112
0.9%
50
0.4%
12,248
100.0%

Sample members with mild ID had the lowest prevalence of autism/ASD. These differences were significant, x2 (4) = 214.9,
N = 11,949, p < .001. Among sample members with autism/ASD, the differences in gender ratio by level of ID were not
significant, x2 (4) = 3.02, N = 950, p > .05.
3.4. Primary means of expression
Sample members with autism/ASD had varied primary means of communication. Five hundred and thirty-three sample
members used spoken language as a primary means of communication, 399 gestures/body language, 15 sign language, 21
communication aid or device and 10 responded ‘‘don’t know.’’ There was a vast difference in primary means of expression
between those with and without and autism/ASD diagnosis, x2 (5) = 269.5, N = 12,290, p < .001, with a lower percentage
using speech (5.8%) than would be expected simply from their representation in the sample (8.1%) and an especially high
percentage of those using communication aids or devices (22.3%).
3.5. Other disability diagnoses
Findings on other disability diagnoses are reported both as raw (univariate) comparisons (alpha = .001), and using
multivariate analysis (logistic regression, alpha = .01) to evaluate the effect of autism/ASD, controlling for age, gender and

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A.S. Hewitt et al. / Research in Autism Spectrum Disorders 6 (2012) 741–751
Table 3
Number and percentage of participants with and without an autism/ASD diagnosis by presence of other characteristics.
Characteristic

Other disability
Mental illness/psychiatric diagnosis

Characteristic
present

No
Yes

Seizure disorder/neurological problem

No
Yes

Vision impairment

No
Yes

Hearing impairment

No
Yes

Physical disability

No
Yes

Communication disorder

No
Yes

Down syndrome

No
Yes

Prader–Willi syndrome

No
Yes

Relationships
Ever married

Never married
Married
Single (married
previously)

Autism diagnosis
No

Yes

Total

Chi-square

7780
91.4%
3600
93.3%
8362
73.5%
3017
26.5%
9516
91.4%
1862
95.2%
10,533
91.8%
844
93.7%
9902
91.4%
1476
96.1%
10,215
92.4%
1163
88.1%
10,215
91.4%
1163
97.8%
11,326
92.0%
51
91.1%

735
8.6%
259
6.7%
721
72.5%
273
27.5%
900
8.6%
93
4.8%
936
8.2%
57
6.3%
934
8.6%
60
3.9%
838
7.6%
157
11.9%
967
8.6%
26
2.2%
988
8.0%
5
8.9%

8515
100.0%
3859
100.0%
9083
73.4%
3290
26.6%
10,416
100.0%
1955
100.0%
11,469
100.0%
901
100.0%
10,836
100.0%
1536
100.0%
11,053
100.0%
1320
100.0%
11,182
100.0%
1189
100.0%
12,314
100.0%
56
100.0%

x2 (1) = 13.25, N = 12,374, p < .001

10,728
95.2%
209
1.9%
278

988
98.8%
4
.4%
5

11,716
95.5%
213
1.7%
283

x2 (3) = 28.71, N = 12,273, p < .001

2.5%

.5%

2.3%

x2 (1) = 0.42 N = 12,373 p = .52

x2 (1) = 33.63, N = 12,371, p < .001

x2 (1) = 3.81, N = 12,370, p < .05

x2 (1) = 40.45, N = 12,372, p < .001

x2 (1) = 29.65, N = 12,373, p < .001

x2 (1) = 60.77, N = 12371, p < .001

x2 (1) = 0.06, N = 12,370, p = .80

a = .001 for univariate analyses.

level of intellectual disability. In the regression analyses all four independent variables were entered simultaneously and
indicator contrasts were used for categorical independent variables, with male and not having autism/ASD serving as the
reference categories.
3.5.1. Psychiatric diagnosis
Overall, there was a significantly smaller percentage of participants with autism/ASD (26.1%) with a psychiatric diagnosis
than those without autism/ASD (31.6%) (see Table 3). However, multivariate analysis (logistic regression) revealed that once
age, level of intellectual disability and gender were taken into account statistically, there was no longer a significant
association between autism/ASD and having a psychiatric diagnosis (Table 4). It was notable that older participants and
those with milder ID were significantly more likely to have a psychiatric diagnosis. As noted, sample members with autism/
ASD were much younger and had more severe disability, which helps explain why the raw comparisons were misleading in
showing that a smaller proportion of people with autism/ASD also had a psychiatric diagnosis. Gender had no significant
multivariate relationship with the presence of a psychiatric diagnosis.
3.5.2. Seizure disorder/neurological problem
There was no significant univariate or multivariate association between autism/ASD and seizure disorder or neurological
problem (Tables 3 and 4). Younger individuals and those with more severe ID were significantly more likely to have a seizure
disorder or neurological problem.

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A.S. Hewitt et al. / Research in Autism Spectrum Disorders 6 (2012) 741–751

Table 4
Results of logistic regression of age, level of intellectual disability, autism/ASD and gender onto other disability diagnoses.
Dependent variable

Independent variables

Wald

B

Odds ratio

Sig.

Nagelkerke
R square

Other disability
Mental illness/psychiatric diagnosis

Seizure disorder/neurological problem

Vision impairment

Hearing impairment

Physical disability

Communication disorder

Down syndrome

Relationships
Ever marrieda

Age
Milder ID
Autism
Female
Age
Milder ID
Autism
Female
Age
Milder ID
Autism
Female
Age
Milder ID
Autism
Female
Age
Milder ID
Autism
Female
Age
Milder ID
Autism
Female
Age
Milder ID
Autism
Female

.015
.194
.080
.052
.011
.469
.178
.020
.010
.227
.599
.038
.019
.140
.124
.024
.004
.471
.936
.060
.008
.714
.305
.064
.017
.148
1.628
.011

113.926
117.958
1.022
1.648
54.205
632.896
4.897
.215
29.861
110.101
26.278
.559
61.730
21.296
.701
.109
3.132
373.086
42.839
1.111
13.475
674.678
9.150
1.045
54.427
30.320
61.898
.033

1.015
1.214
.923
1.053
.989
.626
.837
.980
1.010
.797
.549
1.039
1.019
.869
.883
.977
1.004
.624
.392
1.062
.992
.490
1.356
.938
.983
.862
.196
.989

.000
.000
.312
.199
.000
.000
.027
.643
.000
.000
.000
.455
.000
.000
.402
.741
.077
.000
.000
.292
.000
.000
.002
.307
.000
.000
.000
.855

Age
Milder ID
Autism
Female

.031
1.062
1.193
.833

90.188
272.060
10.689
70.428

1.031
2.892
.303
2.300

.000
.000
.001
.000

.03

.08

.03

.02

.07

.13

.03

.16

Note: Odds ratios > 1.0 denote that the presence of the dependent variable (e.g., other disability) was more likely for participants respectively who were
older, had milder disability, had autism/ASD and were female. a = .01 for multivariate analyses.
a
Ever married recoded as binary for the logistic regression (yes = married now/in the past; no = never married).

3.5.3. Vision impairment
A significantly smaller percentage of participants with autism/ASD (9.4%) had a vision impairment compared to
participants without autism/ASD (16.4%) (Table 3), and this association continued to be significant under multivariate
analysis (Table 4). Individuals who were older and had more severe ID were significantly more likely to have a vision
impairment (Table 4).
3.5.4. Hearing impairment
Based on our chosen significance level of .001 for univariate analyses, there was no significant univariate difference by
autism/ASD diagnosis in the percentage of participants with a hearing impairment (Table 3). Likewise, autism/ASD was not
significantly related to hearing impairment under multivariate analysis, although older participants and those with more
severe ID were significantly more likely to have a hearing impairment (Table 4).
3.5.5. Physical disability
A significantly smaller proportion of people with autism/ASD (6.0%) had a physical disability than those without autism/
ASD (13.0%), a finding that was also confirmed by multivariate analysis (Table 4). Having more severe ID was also a
significant multivariate predictor of physical disability.
3.5.6. Communication disorder
A significantly larger percentage of participants with autism/ASD (15.8%) had a communication disorder, relative to those
without autism/ASD (10.2%) (Table 3). Logistic regression showed that, in addition to autism/ASD, younger age and more
severe ID were also significant predictors of a communication disorder.
3.5.7. Down syndrome
A significantly smaller percentage of participants with autism/ASD (2.6%) had Down syndrome compared to individuals
without autism/ASD (10.2%) (Table 3). This compares with a prevalence of Down syndrome of 9.7% (99% CI = 9.0–10.4%)

A.S. Hewitt et al. / Research in Autism Spectrum Disorders 6 (2012) 741–751

749

among US adult IDD service users reported by Stancliffe et al. (in press). Multivariate analysis showed that Down syndrome
was significantly associated with younger age, more severe ID and not having an autism/ASD diagnosis (Table 4).
3.6. Relationships
3.6.1. Marital status
Very few people included in the sample were currently married or had been married in the past. Even so, there was a
significant difference in the prevalence of autism/ASD by marital status, x2 (3) = 28.71, N = 12, 273, p < .001, with fewer
people with autism/ASD ever married (Table 3). Logistic regression analysis requires a binary dependent variable. Since the
overwhelming majority never married, marital status data were recoded into a binary ever married dependent variable
(yes = married now or in the past; no = never married). Participants were significantly more likely to be married now or in the
past if they were older, had milder intellectual disability, had no autism/ASD diagnosis and were female.
4. Discussion
4.1. Limitations
This study has several limitations. The NCI program requires a standardized approach to surveying that does not allow for
more in depth, individualized exploration of the issues asked about in the survey and the decision-making process used by
respondents in completing their responses. The presence of a diagnosis of autism/ASD on the survey instrument is generally
identified by whether or not the respondent finds a record of such diagnosis in the person’s file. The assessment instruments
and processes used to determine a diagnosis are not recorded in the NCI, which could result in inconsistency in how the
determination of autism/ASD is yielded. It is also possible that some people (particularly older sample members) may have
characteristics of ASD and yet never been given an ASD diagnosis due to changes in diagnostic processes, greater awareness
and an increased identification of co-occurring disabilities in the past decade.
4.2. Demographic characteristics
The percentage of sample members in this study with a diagnosis of autism/ASD averaged 8.1% with a range of 3.2–27.4%
depending upon the state. This finding represents a wide variation that may be explained, in part, by state policy. The lowest
percentage of individuals with autism/ASD existed in states without autism-specific waivers or related conditions eligibility
policies (6.6%), and the five states with both of these polices had the highest percentage of service users with autism/ASD
(9.3%). This suggests that if the program and related policies are tailored to the needs of people with ASD, or if the eligibility
criteria include ASD as a targeted disability category, the program is more likely to serve people with ASD. In the absence of
these state-driven policies it may be more difficult for people with ASD to receive needed supports and services that are
commonly offered by HCBS. This is particularly true for people who have an ASD diagnosis but do not have ID. In the absence
of specific eligibility criteria that do not require a diagnosis of ID, it is unlikely that people with Asperger disorder or high
functioning autism will be served in the developmental disabilities system. It is important to note that irrespective of these
two eligibility policies, each state included in this sample did serve people with ASD in their HCBS waiver and/or ICF/MR
programs. This indicates that at least a certain percentage of people with autism/ASD are being served in the current adult
services system designed for people with intellectual and developmental disabilities.
This study found that male sample members were over three times more likely to have an autism/ASD diagnosis than
females. The male:female ratio was only 1.16 for sample members without autism/ASD but was 3.16 for those with an
autism/ASD diagnosis. However, at 3.16:1 this ratio was somewhat lower than the commonly accepted ASD gender ratio of
between 4:1 and 5:1 (CDC, 2009). Interestingly, among participants with autism/ASD and no ID label, the gender ratio was
higher (4.10:1) than for those with ID (but these differences were not significant), consistent with the proposition that the
more marked gender differences apply to individuals with autism/ASD but without ID, whereas gender ratios for those with
ASD and ID may be smaller (IAN, 2009). The proposition that the gender ratio among people with autism/ASD differs
according to the presence and severity of ID warrants further investigation.
Within this sample there were no significant differences in prevalence of autism/ASD based on race and ethnicity. This
finding is inconsistent with previous studies that have shown an underrepresentation and under-diagnosis (CDC, 2006;
Mandell et al., 2009) or an overrepresentation and over-diagnosis of ASD in children from racial and ethnic minority groups
(Barnevik-Olsson, Gillberg, & Fernell, 2008; Minnesota Department of Health, 2009).
We found a strong overrepresentation of sample members who have a diagnosis of autism/ASD in the youngest age group
(18–29 years). This finding is not unexpected given the increase in the diagnosis of ASD over the past decade and debate
about increased prevalence. Additionally, compared to older participants, there was a notably higher percentage of
individuals with ASD but without ID in the 18–29 age group. We recognize that our cross-sectional data do not directly reveal
trends of service use over time. Even so, if these figures are indicative of likely future growth in new young adult service users
with ASD accessing adult IDD services, then there is clearly a need for IDD services nationally to be prepared to serve
individuals with ASD, including those without ID. It is worth asking the question whether or not individuals with ASD,
particularly those who have ASD but not ID, are appropriately served in traditional services for people with IDD or if there is a

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better option. It is also important to consider whether people with ASD are being served in IDD service systems because other
options are not available.
4.3. Co-occurring disabilities
In this study, sample members with a diagnosis of autism/ASD were more likely to also have a diagnosis of no intellectual
disability or severe/profound ID. This finding is consistent with previous research on the existence of co-occurring non-ASD
developmental diagnoses among children with ASD that show this existence in 41% (CDC, 2009) to 83% (Levy et al., 2010) of
this population. Yet, there is little existing research to explain the increased likelihood for sample members not to have an ID
diagnosis. This finding is perhaps explained by the overall increase in the prevalence of people with ASD in general (CDC,
2010) and the emergence of viewing this disorder on a spectrum with more people being diagnosed with Asperger disorder
who do not have ID. Additionally this finding may be explained by state policies that allow for people with ASD to be served
even if they do not have ID.
Interestingly this study also found that having a diagnosis of autism/ASD was not predictive of an increased co-occurring
hearing, epilepsy or Down syndrome diagnosis. Other studies have found that found that 10% of children with ASD had an
identifiable genetic, neurologic or metabolic disorder, such as fragile X or Down syndrome (Cohen, Pichard, Tordjman,
Baumann, & Burglen, 2005).
4.4. Primary means of expression
A significantly higher percentage of participants with autism/ASD (15.8%) were reported to have a communication
disorder than participants without autism/ASD (10.2%). This was expected based on the characteristics of people with
autism/ASD. Information about each person’s primary means of expression revealed that significantly fewer individuals with
autism/ASD used natural speech (53.4% of participants with autism/ASD; 68.7% without autism/ASD), and a higher
percentage used gestures and body language or a communication aid or device. Despite the substantial percentage of
participants who did not use natural speech, the number who used a communication aid or device was very low (0.8% of the
total sample; 2.1% of those with autism/ASD). It is of concern that uptake of communication aids or devices is so low, because
all individuals have a right to effective communication.
5. Implications
There is a dearth of research on adults with ASD who receive developmental disability services such as HCBS and ICF/MR.
This study provides a snapshot of the characteristics of adults who receive such services in 25 states and sets out important
descriptive information. The findings are in many ways consistent with previous studies on the characteristics of children
and youth with ASD. Yet, they also point to important trends within service delivery, such as the disproportionate number of
younger people (age 18–29 years) with an ASD diagnosis. This finding, along with the growing prevalence of ASD in the
United States (CDC, 2010) likely indicates that there will continue to be growth of people with ASD receiving adult services in
all age groups. The service system will need to develop and implement effective strategies to best serve these individuals
who have unique needs in the areas of communication, social skills and behavior.
Additionally, there are important findings in this study related to state policy and access and utilization of services for
people with ASD. Clearly in states in which there are specific autism HCBS programs and in states that have related clauses in
their eligibility criteria for HCBS programs, a higher percentage of people with autism/ASD are served than in those without
such designated programs. This is particularly important for people with ASD who do not have an intellectual disability but
do have functional limitations for which they need services and support.
Declaration of interest
The Human Services Research Institute (HSRI) employs several of the authors. HSRI coordinates the National Core
Indicators project and receives a fee from participating states. The authors alone are responsible for the content and writing
of the paper.
Acknowledgements
Preparation of this paper was supported by Grant #H133G080029 from the National Institute on Disability and
Rehabilitation Research, U.S. Department of Education (Federal funds for this three year project total $599,998 (99.5% of the
total program costs, with 0% funded by non-governmental sources)).
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