Supplementary information
The impact of comorbidity of intellectual disability on estimates of autism
prevalence among children enrolled in US special education
Andrew Polyak1, Richard M. Kubina2, and Santhosh Girirajan1, 3
1. Department of Biochemistry and Molecular Biology, The Pennsylvania State University,
University Park, PA 16802
2. Department of Education, The Pennsylvania State University, University Park, PA 16802
3. Department of Anthropology, The Pennsylvania State University, University Park, PA
16802
1
Table of Contents
1. Supplemental Tables ................................................................................................................. 3
Table S1: Number of individuals enrolled under different IDEA categories from 2000 to 20103
Table S2. Significance of change in prevalence of disorders (2010 compared to 2000) ............ 3
Table S3: Age-specific change in prevalencea of autism and ID from the IDEA data ............... 4
2. Supplementary Figures ............................................................................................................ 5
Figure S1: Total number of children enrolled under the IDEA program for all the 50 US states
..................................................................................................................................................... 5
Figure S2. Longitudinal analysis to evaluate the changes in prevalence over an 11-year period
for the 13 disease categories under the special education enrollment......................................... 5
Figure S3. Comparison of potential diagnostic change from ID to autism between age groups 6
Figure S4. Age-specific prevalence of autism (ASD) and intellectual disability over a 12-year
period (2000 to 2011) .................................................................................................................. 6
Figure S5. A comparison of Pearson’s correlation coefficients for selected top 5 states with
the lowest and the highest prevalence of ID for the year 2000. .................................................. 7
Figure S6. Negative correlation between the prevalence of autism to that of specific learning
disability ...................................................................................................................................... 7
Figure S7. Percentage of children aged 8 years primarily identified with autism (by ADDM)
for whom special education data were available ......................................................................... 8
References ...................................................................................................................................... 9
2
1. Supplemental Tables
Table S1: Number of individuals enrolled under different IDEA categories from 2000 to 2010
Year
ASD
ID
SLD
DD
OHI
ED
VI
HI
TRA
DEA
OI
MUL
LAN
Total
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
93624
114201
136986
162776
191216
222803
258278
295681
337572
380187
419647
637270
616698
602611
593290
577992
556106
534333
499566
488111
473187
457478
2896318
2866353
2853502
2836262
2803174
2739724
2669257
2572875
2536780
2497581
2427102
21308
24231
28353
30532
33212
33940
33326
35757
35388
36795
38188
304974
350356
403284
463775
520644
570106
610847
640938
666192
698177
725814
481173
483769
486107
489326
489224
477087
464155
441784
421359
408639
391190
29291
28492
28597
28516
28772
28768
29174
29008
29210
29255
29129
78490
77650
78222
78576
79414
79261
79712
78809
79098
79431
79000
15684
21671
22360
23420
24233
24518
24894
24713
25824
25436
25758
1524
1791
1775
1850
1911
1772
NA
1502
NA
NA
NA
83090
83292
83112
76671
73415
70775
69444
67359
70012
65565
63328
132507
136677
138684
139682
140255
140992
142177
138176
131776
132235
131508
1402741
1392725
1412971
1442783
1464298
1469090
1476128
1454906
1451462
1449232
1434928
6177994
6197906
6276563
6367458
6427760
6414942
6391725
6281074
6272784
6275720
6223070
IDEA Categories: ASD=autism; ID=intellectual disability; SLD=specific learning disability; DD=developmental delay; OHI=other health
impairments; ED=emotional disturbance; VI=visual impairment; HI=hearing impairment; TRA=traumatic brain injury; DEA=deafness;
OI=orthopedic impairment; MUL=multiple abnormalities; LAN=speech and language impairment. Complete definition of IDEA categories can be
found in www.ideadata.org.
Table S2. Significance of change in prevalence of disorders (2010 compared to 2000)
IDEA category
Magnitude of prevalence change from 2000-2010 (%) p-value
ASD
331.0
4.58×10-10
ID
-31.0
3.07×10-10
SLD
-19.4
4.05×10-8
ED
-21.8
6.11×10-5
DD
72.4
4.22×10-5
OHI
128.9
2.40×10-8
OI
-26.7
1.02×10-6
LAN
-1.6
0.8337
MUL
-4.6
0.04527
DEA
NA
0.7178
VI
HI
TRA
ASD+ID
ASD+ID+SLD+OHI
-4.4
-3.2
57.9
15.4
-1.4
0.04585
0.007918
0.005316
1.77×10-6
0.1858
Table S3: Age-specific change in prevalencea of autism and ID from the IDEA data
AGE
Change in ASD
Change in ID
Difference in prevalence Fold change in ASD Contribution to diagnostic
prevalence
prevalence
change (ASD+ID)a
(from 2000 to 2010)
recategorization of ID (%)
3
17.87
-7.23
10.64
1.68
40.48
4
26.43
-11.05
15.38
1.72
41.79
5
40.49
-14.57
25.92
1.56
35.98
6
51.56
-18.36
33.20
1.55
35.60
7
62.02
-28.56
33.46
1.85
46.05
8
60.94
-35.94
25.00
2.44
58.98
9
63.54
-38.31
25.24
2.52
60.28
10
61.64
-39.16
22.47
2.74
63.54
11
60.28
-45.76
14.52
4.15
75.92
12
59.18
-47.14
12.05
4.91
79.65
13
54.73
-49.62
5.11
10.72
90.67
14
49.33
-46.96
2.37
20.82
95.20
15
44.83
-43.56
1.27
35.22
97.16
16
41.71
-31.94
9.77
4.27
76.58
17
37.05
-17.47
19.58
1.89
47.15
18
23.69
-9.18
14.52
1.63
38.73
19
11.91
1.65
13.56
0.88
0.00
20
8.84
4.59
13.43
0.66
0.00
21
3.93
3.64
7.57
0.52
0.00
Prevalence measurements are number of affected individuals per 1000 of that age in the general population. The average change in prevalence was
calculated as the sum of change in ASD prevalence/sum of change in ID prevalence and denoted in percentage. The average percentage of diagnostic
change from ages 3 and 18 years is 755.29/484.8=64.18%.
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2. Supplementary Figures
A
B
600000
Number of children enrolled
Prevalence (out of 10,000)
1000
800
600
400
200
400000
200000
10
09
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
20
08
20
07
20
06
20
05
20
04
20
02
03
20
20
20
20
20
01
0
00
0
Age (years)
Figure S1: Total number of children enrolled under the IDEA program for all the 50 US
states. (A) The total enrollment (out of 10,000) is shown for years from 2000 to 2010. (B) Agespecific counts of enrolled children under IDEA are depicted for the year 2010. The data are
missing for several states at multiple year and age points. Therefore, US population estimates
were used as denominators for frequency calculations.
Proportion of enrolled students
(out of 10,000)
600
ASD+ID+SLD+OHI
ASD
ID
SLD
ED
400
DD
OHI
OI
LAN
MUL
200
DEA
VI
HI
TRA
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
0
Figure S2. Longitudinal analysis to evaluate the changes in prevalence over an 11-year
period for the 13 disease categories under the special education enrollment. Analysis of
prevalence of neurodevelopmental phenotypes under the enrollment categories suggested upward
as well as downward trends. As assessed by linear regression, significant increase in prevalence
was observed for other health impairments (128%, linear regression, p=2.4×10-8) and traumatic
brain injury (58%, p=0.005). However, significant decrease in prevalence was observed for
intellectual disability (31%, p=3.1×10-10), emotional disturbance (22%, p=6.1×10-5), and specific
learning disability (19%, p=4.1×10-8). Combined prevalence of ASD+ID+SLD+OHI does not
show a significant increase (1.4%, p=0.19).
150
100
50
s
ar
ye
ye
ar
s
0
10
-1
3-
8
9
Prevalence change from 2000 to 2010
(out of 10,000)
Age comparison of potential
shift of diagnosis from ID to autism
Figure S3. Comparison of potential diagnostic change from ID to autism between age
groups.
Prevalence (out of 10,000)
Autism
100
80
60
40
20
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
0
B
Prevalence (out of 10,000)
A
Intellectual disability
150
100
50
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
0
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Figure S4. Age-specific prevalence of autism (ASD) and intellectual disability over a 12year period (2000 to 2011) as assessed from special education enrollment is shown.
6
-0.6
-0.8
-1.0
ig
H
Lo
w
es
he
st
5
-1.2
t5
Correlation coefficient
-0.4
Figure S5. A comparison of Pearson’s correlation coefficients for selected top 5 states with
the lowest and the highest prevalence of ID for the year 2000. Mann Whitney test was
performed with one-tailed p-value of 0.0476. The Y-axis shows correlation coefficients for US
states (see Table S5) with the lowest prevalence of ID (New Jersey, Colorado, New Hampshire,
New York, Maine) and the US states with the highest prevalence of ID at year 2000 (Arkansas,
Alabama, Kentucky, Ohio and West Virginia).
Figure S6. Negative correlation between the prevalence of autism to that of specific
learning disability (r=-0.28, p<0.0001) Pearson correlation coefficients were used to assess the
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relationship between the prevalence of autism and each of the comorbid phenotypic categories
within the special education enrollment.
100
Autism/preschool developmental delay
Autism/hearing or visual impairments
Autism/multiple disabilities
Autism/other health impairments
Utah
North Carolina
New Jersey
Maryland
Georgia
20
0
Utah
South Carolina
North Carolina
New Jersey
Maryland
Georgia
Colorado
0
Arkansas
20
40
Colorado
40
60
Arkansas
60
80
Arizona
Autistic individuals with
comorbid phenotypes (%)
80
Arizona
Autism individuals under
special education data (%)
100
Autism/emotional disturbance
Autism/specific learning disability
Autism/intellectual disability
Autism/speech or language impairments
Autism
Figure S7. Percentage of children aged 8 years primarily identified with autism (by
ADDM) for whom special education data were available. Frequency of comorbid features
among individuals primarily ascertained for autism within the Autism and Developmental
Disability Monitoring network1 2 are shown. Shown are (A) autism prevalence data for the year
2008 and (B) data for the year 2010. Data from Baio et al, 20121, and 20142 were used to derive
these graphs.
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REFERENCES
1. Autism, Developmental Disabilities Monitoring Network Surveillance Year Principal I,
Centers for Disease C, et al. Prevalence of autism spectrum disorders--Autism and
Developmental Disabilities Monitoring Network, 14 sites, United States, 2008. MMWR
Surveill Summ 2012;61(3):1-19.
2. Autism, Developmental Disabilities Monitoring Network Surveillance Year Principal I,
Centers for Disease C, et al. Prevalence of autism spectrum disorder among children aged
8 years - autism and developmental disabilities monitoring network, 11 sites, United
States, 2010. MMWR Surveill Summ 2014;63(2):1-21.
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