B R I E F R E P O R T

Brief Report: Concurrent Validity of Autism Symptom Severity Measures

Stephanie S. Reszka • Brian A. Boyd •

Matthew McBee • Kara A. Hume • Samuel L. Odom

Published online: 27 June 2013

� Springer Science+Business Media New York 2013

Abstract The autism spectrum disorder (ASD) diagnos-

tic classifications, according to the DSM-5, include a

severity rating. Several screening and/or diagnostic mea-

sures, such as the autism diagnostic and observation

schedule (ADOS), Childhood Autism Rating Scale (CARS)

and social responsiveness scale (SRS) (teacher and parent

versions), include an assessment of symptom severity. The

purpose of this study was to examine whether symptom

severity and/or diagnostic status of preschool-aged children

with ASD (N = 201) were similarly categorized on these

measures. For half of the sample, children were similarly

classified across the four measures, and scores on most

measures were correlated, with the exception of the ADOS

and SRS-P. While the ADOS, CARS, and SRS are reliable

and valid measures, there is some disagreement between

measures with regard to child classification and the cate-

gorization of autism symptom severity.

Keywords Concurrent validity � Autism � Severity � Diagnostic classification

Introduction

The proposed changes to the forthcoming diagnostic and

statistical manual of mental disorders, DSM-5 (http://

www.dsm5.org) would include severity criteria for the

autism spectrum disorders (ASD) category. This new cri-

teria would combine autism disorder, Asperger syndrome,

and pervasive developmental disorder—not otherwise

specified (PDD-NOS) into one larger ASD category. As a

result of this collapse, reliable and valid measurement of

autism severity will be even more important in the deter-

mination of services for children with a diagnosis of ASD

(Matson et al. 2012).

Currently, the Childhood Autism Rating Scale (CARS;

Schopler et al. 1986) and Social Responsiveness Scale

(SRS; Constantino 2002) are two commonly used measures

that include a symptom severity estimate. Previously,

higher raw scores on the autism diagnostic and observation

schedule (ADOS; Lord et al. 1999) indicated the presence

of more deficits that are characteristic of individuals with

ASD, suggesting a greater level of impairment, but the raw

scores were not normalized to indicate severity (Gotham

et al. 2009). A recent calibrated severity metric provides

estimations of ASD symptom severity using ADOS scores

(see Gotham et al. 2009). Generally, severity is measured

in several areas for children with ASD: language delay,

cognitive functioning, and behavioral issues (Gotham et al.

2009), however these are not necessarily considered the

core features of ASD. Each of these measures, the CARS,

SRS, and ADOS utilizes slightly different methods of

evaluating the severity of ASD symptoms and have varied

diagnostic cut-offs along the ASD spectrum.

The primary purpose of this study was to examine

whether children’s symptom severity and/or diagnostic

status were similarly categorized across the four measures.

S. S. Reszka (&) � B. A. Boyd Department of Allied Health, Division of Occupational Science

and Occupational Therapy, University of North Carolina, 321 S.

Columbia Street, Bondurant Hall CB #7122, Chapel Hill,

NC 27599-7122, USA

e-mail: [email protected]

Present Address:

M. McBee

East Tennessee State University, Johnson City, TN, USA

M. McBee � K. A. Hume � S. L. Odom Frank Porter Graham Child Development Institute, University

of North Carolina, Chapel Hill, NC, USA

123

J Autism Dev Disord (2014) 44:466–470

DOI 10.1007/s10803-013-1879-7

The two study goals were to examine: (1) the concurrent

validity of the ADOS, CARS, and SRS (parent and teacher

versions) and (2) the categorization of children’s diagnostic

status and symptom severity.

Methods

Data for this study were collected on 201 children as part of a

larger study comparing the efficacy of school-based, com-

prehensive treatment models for preschoolers with ASD.

Data were collected across four states (CO, NC, FL, and

MN), and at the beginning of the school year. For each child,

all measures were collected within a 6-week time window.

Participants

Children

At enrollment, the mean child age was 3.59 years (SD = 0.56,

range 2.24–5.04). Most participating children were male

(83.3 %) and ethnically non-Hispanic (64.6 %). In terms of

racial status, 5.1 % were identified as Asian, 12.1 % were

Black, 78.3 % were White, and 4.0 % were multiracial. To be

eligible for the larger study, each child was required to have a

clinical or school diagnosis of autism, PDD-NOS, or Asper-

ger’s Syndrome, or meet the autism spectrum cut-off score on

the ADOS and Social Communication Questionnaire (SCQ;

Rutter et al. 2003). If the child had an educational label of

developmental delay (DD) instead of ASD, which is consis-

tent with federal and state policy for children in this age range,

then s/he must have met diagnostic criteria on both the ADOS

and SCQ to be eligible for the study. It was not the point of our

study to diagnose children, but rather screen them for potential

eligibility and a DD educational label is reflective of the real-

world heterogeneity when recruiting children through local

school systems. The other study measures included the fol-

lowing: (1) Mullen Scales of Early Learning (Mullen 1995),

which is a measure of children’s cognitive and motor devel-

opment. Trained research staff administered the visual

reception, fine motor, expressive language, and receptive

language subscales to the child. The mean standard score on

the Mullen was 64.40 (N = 193, SD = 19.6, range 49–136).

And (2) Preschool Language Scale, fourth edition (PLS-4;

Zimmerman et al. 2003), which is a measure of children’s

auditory comprehension and expressive communication

skills. The mean standard score on the PLS-4 was 68.23

(N = 198, SD = 68.23, range 50–134).

Parents

Most participating parents were female (88.2 %), non-

Hispanic (66.8 %). Additionally, 5.2 % were identified as

Asian, 13.0 % were black, 78.7 % were white, and 3.1 %

were multiracial. Household annual income ranged from

less than $20,000 (12.8 %) to over $100,000 (26.7 %).

Parents completed the parent version of the SRS (SRS-P).

Teachers

Teachers completed the teacher version of the SRS (SRS-

T). Participating teachers were almost exclusively female

(98.6 %) and non-Hispanic (83.6 %), and identified them-

selves as white (97.3 %), with the remaining 2.7 % iden-

tifying themselves as black. most held a master’s degree

(56.2 %), while 37 % had a bachelor’s, 2.7 % had an

associate’s, and 4.1 % had a degree above the master’s

level.

Diagnostic and Severity Measures

The measures examined in this study included the ADOS,

CARS, and SRS parent and teacher versions. Both the

ADOS and CARS were administered by trained and reli-

able project staff. The ADOS was administered by a

research-trained and/or research reliable staff member at

each site, and staff across sites met reliability criterion on a

series of CARS training tapes prior to administration.

The ADOS is a semi-structured assessment of children’s

communication, social, and play skills. Module 1 is for

children who are non-verbal or who have a few words.

Module 2 is for children with phrase speech, while Module

3 is intended for children who are verbally fluent. In

accordance with the suggested severity ratings, ADOS

severity scores of 4–5 indicated autism spectrum disorder

and scores from 6 to 10 indicated autism (Gotham et al.

2009). In this sample, 125 children were administered

Module 1 of the ADOS, 57 were administered Module 2,

and 15 were administered Module 3, while 4 children had

missing data for the ADOS.

Using the CARS, the child is rated on 15 subscales

based on observation (during the Mullen administration, in

this case). To ensure consistency in CARS scoring across

study sites and classrooms, the measure was completed

based on observations of children’s behavior during the

structured administration of the Mullen and 15 min of

unstructured time post-Mullen administration. The CARS

includes items on socialization, communication, emotional

response, and sensory issues. Each of the 15 items is rated

on a scale from 0 to 4, with 4 indicating severe impair-

ments. A CARS cutoff raw score of 25.5 was used to

indicate autism spectrum disorder, with raw scores over 30

indicating autism (Chlebowski et al. 2010). The original

CARS was used, as opposed to the newly released CARS2

(Schopler et al. 2010), because the CARS2 only became

publicly available after the study was already underway.

J Autism Dev Disord (2014) 44:466–470 467

123

This study used the original CARS, which is aligned with

the currently available CARS2-ST, for children younger

than 6 years of age.

The SRS is a 65-item rating scale that was completed by

parents and teachers. The SRS provides information about

children’s social functioning including social awareness,

social information processing, social reciprocal communi-

cation, social anxiety/avoidance behaviors, and stereotypic

behavior/restricted interests. Each item is rated on a scale

of 1 (not true) to 4 (almost always true). T-scores (mean of

50, standard deviation of 10) were used in the analyses,

with a T-score of 60–75 indicating mild to moderate

symptoms of ASD, and scores over 75 indicating severe

symptoms. The SRS was normed with T-scores for parent

and teacher versions, with separate norms within each for

child gender. The appropriate scoring norms were used for

each measure, as specified by the SRS manual. The pre-

school version of the SRS was used for children aged

36–47 months, and the standard version was used for

children 48 months and older.

Results

Autism diagnostic and observation schedule scores ranged

from 2 to 10, with a mean of 7.19 (SD = 1.64) suggesting

that children in the sample tended to score in the milder

end of the ASD category, but represented the full range of

severity across the spectrum. The mean score on the CARS

was 33.37 (SD = 7.31) with a range of 15–55.5. Similarly

to the ADOS mean score, the mean score of 33.37 corre-

sponds to the autism category for the CARS. The SRS-

Teacher (SRS-T) version and SRS-Parent (SRS-P) versions

both showed mean scores in the mild to moderate symptom

category (66.27 and 73.70, respectively). Descriptive

information for each measure is available in Table 1.

Question 1: Concurrent Validity at Pretest

The ADOS severity scores were significantly correlated

with the CARS total score (r = 0.432, p 0.001) and the total score on the teacher version of the SRS (r = 0.418,

p 0.001). The ADOS severity scores were not signifi- cantly correlated with scores on the SRS-P (r = 0.088,

p = 0.236). The CARS was significantly correlated with

both versions of the SRS (r = 0.558, p 0.001 for the teacher version; r = 0.292, p 0.001 for the parent ver- sion). The SRS-Teacher and SRS-Parent scores were sig-

nificantly correlated (r = 0.275, p 0.001). The correlation matrix for these measures is shown in Table 2.

Question 2: Categorization of Diagnostic Status/

Severity

Nearly 98 % of the children scored on the spectrum

according to the ADOS. The CARS scores classified

64.7 % of children as being on the spectrum. The SRS-

Teacher and SRS-Parent scores classified 76.6 and 82.1 %

of children as being on the spectrum, respectively. Diag-

nostic classification charts for each measure are available

in Fig. 1.

A summary of children’s diagnostic classifications

across all measures is available in Table 3. Ratings were

collapsed so that a score of 0 indicated that the child did

not score on the autism spectrum, while a score of 1

indicated that a child would score in the autism spectrum

range (mild/moderate/severe autism symptoms). As shown,

for 92 cases (50 % of the sample) children were classified

similarly across all measures. For another 25 cases

(13.59 % of the sample), children were classified similarly

on the ADOS and both versions of the SRS, but not the

CARS. The remaining children scored on the spectrum on

one or more of the measures. Almost 14 % scored on the

spectrum according to the ADOS and both SRS versions,

but not the CARS, followed by 10.33 % on the ADOS and

SRS-Parent only. Another 6.52 % of children scored on the

spectrum on the ADOS, CARS, and SRS-Parent. Approx-

imately 6 % scored on the spectrum on both the ADOS and

SRS-Teacher and another nearly 6 % on the ADOS,

CARS, and SRS-Teacher. Almost 4 % scored on the

spectrum only on the ADOS. Just over 2 % scored on the

spectrum only on the ADOS and CARS. Finally, 1 % of

children scored on the spectrum according to the SRS-

Parent and SRS-Teacher forms only, and 0.54 % scored on

the spectrum only on the SRS-Parent. For approximately

76 % of the sample (140 cases), children were similarly

classified on at least three of the four measures.

Table 1 Descriptives for measures

Measure N Mean (SD) Range

ADOS severity 198 7.19 (1.64) 2.00–10.00

CARS total score 200 33.37 (7.31) 15.00–55.50

SRS-Teacher total score 200 66.27 (9.66) 42.00–90.00

SRS-Parent total score 185 73.70 (14.27) 42.00–111.00

Table 2 Bivariate correlations of measures

ADOS severity

Score

CARS total

score

SRS-

Teacher

CARS total score 0.432 (.001) – – SRS-Teacher total

score

0.418 (.001) 0.558 (.001) –

SRS-Parent total

score

0.088 (.236) 0.292 (.001) 0.275 (.001)

p values in parentheses

468 J Autism Dev Disord (2014) 44:466–470

123

Discussion

Generally, children’s severity scores on the measures were

correlated, indicating that the severity of autism symptoms

was rated similarly across all measures, with the exception

of the ADOS and SRS-Parent version. There were mod-

erate to strong correlations between the CARS and all other

measures, and between the SRS-T and all other measures.

The ADOS was moderately correlated with both the CARS

and SRS-T, but not with the SRS-P. Research suggests that

scores on the SRS agree with clinical diagnosis a signifi-

cant portion of the time and the SRS teacher and parent

versions have shown correlations ranging from 0.75 to 0.91

in a clinical sample (Constantino et al. 2003), while this

sample showed a weaker, but still significant, correlation of

0.275. Interestingly, the parent version of the SRS was

correlated, albeit moderately, with all other measures with

the exception of the ADOS. However, the statistical

significance of some of the more modest correlations may

be an artifact of the relatively large sample size used in this

study.

The differences in ADOS and SRS-Parent scores seen in

this study may reflect potential variations in child behaviors

across different contexts; all measures except the SRS-P

were completed in the school context, while the SRS-P

reflects parental views of child behaviors at home. It is

important to consider the context under which these mea-

sures of symptom severity were collected. The parent

measures were not always correlated with measures taken

in the school context by teachers or research staff, and

children may display different behaviors at home than they

would in a classroom or research setting. Thus the context

may be a factor in potential disagreements between par-

ents’ and clinicians’ or practitioners’ interpretations of

symptom severity or autism diagnosis.

For half of the sample, children were similarly classified

across all measures. About three quarters (76 %) of the

sample were similarly classified on at least three of the four

measures. Ratings on the CARS appear to be the most

conservative regarding diagnosis, as only 64.7 % (119

children) were rated as having an ASD diagnosis using the

CARS, while nearly all (98.4 %; 181 out of 184) of the

children were rated as having a diagnosis on the spectrum

according to the ADOS. However the ADOS, along with

the SCQ, was used to determine children’s study eligibility,

and was selected because it is considered a gold-standard

measure for ASD diagnosis.

While the children in this study were between the ages

of 3 and 5, previous research comparing the ADOS and

CARS for diagnosing toddlers with ASD suggests that

there is a significant agreement between the two for diag-

nosing ASD in toddlers, matching clinical judgment

(Ventola et al. 2006). Children in this study tended to have

Fig. 1 Diagnostic classification pie charts by measure

Table 3 Collapsed summary of diagnostic ratings

ADOS CARS SRS-Teacher SRS-Parent N %

0 0 0 1 1 0.54

0 0 1 1 2 1.09

1 0 0 0 7 3.80

1 0 0 1 19 10.33

1 0 1 0 11 5.98

1 0 1 1 25 13.59

1 1 0 0 4 2.17

1 1 0 1 12 6.52

1 1 1 0 11 5.98

1 1 1 1 92 50.00

184 100.00

17 cases were missing and not included in the analysis. 0 = not

autistic/not on spectrum, 1 = on spectrum/mild autism/severe autism

J Autism Dev Disord (2014) 44:466–470 469

123

mild to moderate symptoms of autism. The CARS is better

at diagnosing children who tend to be lower functioning

than those who are higher functioning (Mayes et al. 2009),

which may explain some of the discrepancy between

CARS classification and the other measures. A newly

released version of the CARS (CARS2-HF) assesses ver-

bally fluent, more high-functioning children, but currently

is only available for children age 6 and older.

The proposed changes to the DSM-5 include severity

criteria for the ASD category, allowing ratings of symp-

toms along ‘‘a continuum from mild to severe rather than a

simple yes or no diagnosis to a specific disorder’’ (APA

2012). Given these changes, measures of symptom severity

may become more critical in autism research and clinical

practice. While the severity measures used in this study

may not match the severity criteria in the proposed DSM-5,

this study is a first step toward examining the agreement, or

lack thereof, of commonly used measures of autism

symptom severity. Additional future studies should exam-

ine the relationships between the current measures of

severity described in this study with the severity classifi-

cations that will be found in the DSM-5.

While there are instruments that can produce reliable

and valid assessments of autism severity available, this

study demonstrates that there is some disagreement among

several of these measures with regard to child classifica-

tions and the categorization of symptom severity. The type

of measure used could affect child classifications, and by

extension, services provided to these children.

Acknowledgments This research was supported by the Institute of Education Sciences (R324B070219).

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Introduction

The most recent edition of the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5) introduced substantial revisions to the diagnostic criteria for autism (American Psychiatric Association, 2013). Key changes included a shift from triadic to dyadic symptom group- ings, and a consolidation of previously separate diag- nostic subcategories (i.e. autistic disorder, Asperger’s disorder, and pervasive developmental disorder not other- wise specified) into a single category of autism spectrum disorder (ASD). These primary changes have received a great deal of attention from scientific, clinical, and lay communities, primarily focused on concern about poten- tial effects on prevalence estimates and service eligibility (Buxbaum and Baron-Cohen, 2013; Grzadzinski et al., 2013; Halfon and Kuo, 2013; Volkmar and Reichow, 2013). As a result, a number of studies of sensitivity, spec- ificity, and diagnostic concordance between DSM-IV and DSM-5 have been conducted since the draft criteria were

first released (see, for review, Kulage et al., 2014; Smith et al., 2015). By contrast, the addition of severity level ratings, an equally significant change to the diagnostic criteria for ASD, has received little scientific attention.

As noted above, changes to DSM-5 were intended, in part, to address problems with inter-rater agreement on DSM-IV subcategories (Lord and Bishop, 2015; Ozonoff

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