Age at diagnosis of autism spectrum disorders in four regions of Canada.

Autism spectrum disorders--which include autistic disorder, pervasive developmental disorder-not otherwise specified (PDD-NOS) and Asperger's disorder (1)--are a group of neurodevelopmental disorders that are characterized by marked impairments in social functioning and communication, as well as repetitive patterns of behaviour or restricted interests. Early intervention programs, which aim to help children modify their behaviour and learn new skills, are a widely used treatment for autism spectrum disorders (hereinafter referred to as "autism"). Some studies have reported greater improvements when children enter these programs at a younger age, (2,3) and a recent report from the Centers for Disease Control and Prevention states: "Given the benefit of early intervention, identification of an ASD [autism spectrum disorder] at earlier ages in the United States is essential to ensure that children receive optimal early intervention services." (4) Early diagnosis also helps to reduce the confusion and stress parents experience when they do not understand the reasons for their child's behaviour, (5) and empowers them to make choices such as seeking genetic counseling.

In many cases, autism can be diagnosed reliably between two and three years of age,(6-9) although often children are not identified until they are older. (10-14) Several studies have reported decreases in the age at which children are diagnosed with autism when comparing birth cohorts (15,16) or year of diagnosis, (17) while other studies have found an increase in age at diagnosis across birth cohorts (although not statistically significant), (12) or no clear trend over time. (18) Geographic differences have also been reported. For example, the median age at first autism diagnosis ranged from 49 months in Utah to 66 months in Alabama, based on surveillance data for children who were 8 years old in 2002. (4)

There is little information on the age at which Canadian children are first diagnosed with autism, apart from one study that used administrative data to estimate the prevalence of autism among children in Manitoba and Prince Edward Island (PEI) in 2002. In those provinces, the median age at diagnosis was 3.7 and 3.6 years, respectively. (19) The objectives of the current analysis were to determine: 1) the age at which children in various regions of Canada are first diagnosed with autism; 2) whether geographic variations in age at diagnosis exist; and 3) whether there is a trend towards earlier diagnosis in more recent years. We also examined whether there are differences in age at diagnosis between boys and girls and across diagnostic subtypes.

METHODS

Data source and sample

The National Epidemiologic Database for the Study of Autism in Canada (NEDSAC) was established in 2001. It functions as a surveillance program for diagnosed cases of autism among children in various regions of Canada. Because the delivery of health, social services and education differs across provinces, different protocols were adopted in the surveillance regions with the goal of achieving maximum case ascertainment in the most cost-effective manner possible (see Table 1). Ethics approval was obtained from the PEI Research Ethics Board, and from research ethics boards at the University of Manitoba, Queen's University, and Memorial University for ongoing surveillance in PEI, Manitoba, Southeastern Ontario, and Newfoundland and Labrador, respectively. NEDSAC contains the date of birth and sex of all children identified by participating agencies in the surveillance regions. Depending on the amount of information that is available in files (Manitoba), or whether the family consents to provide more detailed information to the research team (Southeastern Ontario, PEI, Newfoundland and Labrador), the database also contains information on whether the child is adopted, number of siblings and number of siblings with autism, first three digits of the postal code of the child's current residence, birthplace, maternal and paternal age, ethno-cultural identity, diagnostic subtype, date of diagnosis, who made the diagnosis, and the tests that were used.

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For the current analysis, we included children identified for NEDSAC from the time data collection began (2002 in Manitoba and PEI; 2003 in Southeastern Ontario and Newfoundland and Labrador) up until May 2007, who: 1) were first diagnosed with autistic disorder, PDD-NOS, Asperger's disorder, or a non-specific diagnosis of autism spectrum disorder between 1997 and 2005, inclusive, and whose month of diagnosis was known; and 2) were born in one of the surveillance regions and still living there in the year when diagnosed, or, if they were born elsewhere, diagnosed either in the same year they moved to the surveillance region or in a subsequent year.

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Analysis

Age at diagnosis is reported using medians and interquartile ranges due to the variable's skewed distribution (see Figures 1-5). We used SPSS 16.0.1 (SPSS Inc., Chicago, IL) and the Mann-Whitney or Kruskal-Wallis test to compare inter- and intra-regional findings for age at diagnosis by sex and diagnostic subtype (i.e., autistic disorder, PDD-NOS, Asperger's disorder, or general diagnosis on the autism spectrum ("ASD")), and inter-regional differences by three-year period in which the initial diagnosis was made (1997-1999, 2000-2002, 2003-2005). The Spearman's rank correlation was used to examine intra-regional trends by three-year period of initial diagnosis. For Manitoba--the only region with a sufficient sample size to conduct a stratified analysis--we also examined, for each diagnostic subtype, whether the age at diagnosis increased or decreased significantly by three-year period of initial diagnosis, using Spearman's rank correlation. All references to significance are based on two-tailed tests using an alpha of 0.05. We did not consider any adjustment of this alpha level for multiple testing because of the exploratory nature of the study.

RESULTS

Figures 1-5 illustrate the distribution of age at diagnosis for the combined sample and for each region. Table 2 reveals significant inter-regional differences in the median age at diagnosis overall (p<0.001) and for boys (p<0.001). Girls were diagnosed later than boys in all regions, although none of the differences was significant. The age at diagnosis differed significantly across regions for two time periods: 2000-2002, and 2003-2005. In Southeastern Ontario, it increased significantly over time (p = 0.004).

Significant inter-regional differences were observed for the median age at diagnosis of PDD-NOS and ASD. The age at which children were diagnosed with PDD-NOS was highest in Manitoba (77.0 months) and lowest in Newfoundland and Labrador (48.0 months). For the ASD category, Southeastern Ontario had the highest median age of diagnosis at 47.0 months, compared to 36.0 months for Newfoundland and Labrador. Significant differences in age at diagnosis for the diagnostic subtypes were found within all regions. Children with autistic disorder or ASD were diagnosed the earliest, followed by those with PDD-NOS. Children with Asperger's disorder were more likely to be diagnosed when they were older. For almost all the subgroup analyses, Newfoundland and Labrador had the lowest age at diagnosis. The only exception was for autistic disorder, which was diagnosed earliest in Southeastern Ontario (34.0 months).

Table 3 shows that there was a significant increase over time in the median age at diagnosis of PDD-NOS in Manitoba (p = 0.021). An increase over time was also observed for Asperger's disorder in that province, but it was not significant.

DISCUSSION

The Senate Standing Committee on Social Affairs, Science and Technology, in its final report on the enquiry into funding autism treatment in Canada, noted there are waiting times for assessment and diagnosis, and parents frequently are "unable to access timely assessment and diagnosis of their children". (20) Although many cases of autism can be diagnosed reliably between two and three years of age, (6-9) in three of the surveillance regions (Manitoba, Southeastern Ontario, PEI) about half the children were not diagnosed until four years of age or more.

Overall, Newfoundland and Labrador had the lowest median age at diagnosis. In that province, there is a "zero" waitlist policy for early intervention for preschool children diagnosed with autism. There may be more incentive for earlier diagnosis in regions with reduced waiting times for services. In contrast, Southeastern Ontario had the highest median age at diagnosis. One possible explanation for this is the large proportion of children identified with Asperger's disorder in that region (24.8%) compared to elsewhere (less than 12%). In all regions, consistent with findings from other studies, (10,14,15,21) children with Asperger's disorder were diagnosed later than children with PDD-NOS or autistic disorder.

Southeastern Ontario had the highest median age at diagnosis overall, yet children with autistic disorder were diagnosed earlier there than in any other region. Any child with autism who meets the age criteria is eligible for provincially funded intensive behavioural intervention programs in Manitoba, PEI, and Newfoundland and Labrador. In contrast, only children with autistic disorder or those on the severe end of the autism spectrum are eligible for the program in Ontario. (22) One hypothesis for the anomalous finding for age at diagnosis of autistic disorder in Southeastern Ontario then is that assessment resources tend to be focused on the more severe cases, who may be eligible for provincially funded early intervention services.

Southeastern Ontario was also the one region where the age at diagnosis increased over time. In Manitoba, where the sample size was sufficient to conduct an analysis of age at diagnosis stratified by diagnostic subtype and year of initial diagnosis, temporal increases in age at diagnosis were observed for Asperger's disorder and for PDD-NOS. One possible explanation for these findings is that older, higher-functioning children who were not diagnosed in the past may be more likely to receive an autism diagnosis as awareness of the autism spectrum increases.

Several cautions and limitations of the methods need to be taken into account when interpreting the findings. Some investigators have compared birth cohorts when examining whether the age at which children are diagnosed with autism is decreasing. (12,15,16) We chose to use calendar years instead, as children who were born in more recent years (e.g., late 1990s and early 2000s) may not yet have been diagnosed with autism, which would bias the results towards a younger age at diagnosis in later birth cohorts. Accordingly, it is not possible to directly compare our findings with those from studies that have examined age at diagnosis for birth cohorts. It is also important to note that the analysis presented in this paper did not include all children who were diagnosed with autism between 1997 and 2005 in the surveillance regions. NEDSAC does not contain information on children who moved from the surveillance regions before data collection began in 2002/2003. It is unlikely, however, that migration is related to age at diagnosis, and therefore the non-inclusion of these children would probably not affect the findings greatly. We also excluded from the analysis cases for whom the month or year of diagnosis were unknown, as well as cases whose residence in the surveillance regions during or prior to the year in which they were diagnosed could not be confirmed. To assess what effect the exclusion of these two groups of children might have on the findings, we examined the age and sex of children who were included and excluded from the analysis. No significant sex differences were detected between the groups. However, in all regions the group that was excluded from the analysis was significantly older than the group that was included. Since current age of the child was significantly and inversely correlated with year of diagnosis in all regions, the children who were excluded from the analysis were more likely to have been diagnosed before 1997 and hence would not have met the inclusion criteria, or to have been diagnosed during the first three-year interval of the study period. Accordingly, the findings for 1997-1999 are where the greatest potential for bias exists.

While a discussion of diagnostic procedures over the study period is beyond the scope of this paper, it is probable that there were differences among regions as well as within each region over time in terms of the diagnostic criteria, types of professionals, and methods used to make the diagnosis. Regardless of how the diagnosis was made, however, early diagnosis is important for all the reasons mentioned in the introduction, and our findings suggest that children with autism are not being diagnosed at as young an age as the literature suggests they could be. Further study is warranted to understand the factors contributing to delays in diagnosis. Such research would inform best practices for early identification of autism and timely access to treatment and supports.

Acknowledgements: This work was supported by an Interdisciplinary Health Research Team Grant from the Canadian Institutes of Health Research (#43820) to the Autism Spectrum Disorders Canadian-American Research Consortium (ASD-CARC) (J.J.A. Holden, Principal Investigator) and an Operating Grant from the Canadian Institutes of Health Research (#79556) to H. Ouellette-Kuntz.

Received: May 9, 2008

Accepted: January 9, 2009

REFERENCES

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(3.) Fenske EC, Zalenski S, Krantz PJ, McClannahan LE. Age at intervention and treatment outcome for autistic children in a comprehensive intervention program. Analysis and Intervention in Developmental Disabilities 1985;5:49-58.

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(5.) Midence K, O'Neill M. The experience of parents in the diagnosis of autism: A pilot study. Autism 1999;3(3):273-85.

(6.) Turner LM, Stone WL, Pozdol SL, Coonrod EE. Follow-up of children with autism spectrum disorders from age 2 to age 9. Autism 2006;10(3):243-65.

(7.) Moore V, Goodson S. How well does early diagnosis of autism stand the test of time? Follow-up study of children assessed for autism at age 2 and development of an early diagnostic service. Autism 2003;7(1):47-63.

(8.) Cox A, Klein K, Charman T, Baird G, Baron-Cohen S, Swettenham J, et al. Autism spectrum disorders at 20 and 42 months of age: Stability of clinical and ADI-R diagnosis. J Child Psychol Psychiatry 1999;40(5):719-32.

(9.) Stone WL, Lee EB, Ashford L, Brissie J, Hepburn SL, Coonrod EE, et al. Can autism be diagnosed accurately in children under 3 years? J Child Psychol Psychiat 1999;40(2):219-26.

(10.) Howlin P, Asgharian A. The diagnosis of autism and Asperger syndrome: Findings from a survey of 770 families. Dev Med Child Neurol 1999;41:834-39.

(11.) Lingam R, Simmons A, Andrews N, Miller E, Stowe J, Taylor B. Prevalence of autism and parentally reported triggers in a north east London population. Arch Dis Child 2003;88:666-70.

(12.) Magnusson P, Saemundsen E. Prevalence of autism in Iceland. J Autism Dev Disord 2001;31(2):153-63.

(13.) Mandell D, Listerud J, Levy SE, Pinto-Martin JA. Race differences in the age at diagnosis among Medicaid-eligible children with autism. J Am Acad Child Adolesc Psychiatry 2002;41(12):1447-53.

(14.) Wiggins LD, Baio J, Rice C. Examination of the time between first evaluation and first autism spectrum diagnosis in a population-based sample. J Dev Behav Pediatr 2006;27(2):S79-S87.

(15.) Chakrabarti S, Fombonne E. Pervasive developmental disorders in preschool children: Confirmation of high prevalence. Am J Psychiatry 2005;162(6):1133-41.

(16.) Keen D, Ward S. Autistic spectrum disorder: A child population profile. Autism 2004;8(1):39-48.

(17.) Latif AHA, Williams WR. Diagnostic trends in autistic spectrum disorders in the South Wales valleys. Autism 2007;11(6):479-87.

(18.) Kaye JA, del Mar Melero-Montes M, Jick H. Mumps, measles and rubella vaccine and the incidence of autism recorded by general practitioners: A time trend analysis. BMJ 2001;322:460-63.

(19.) Ouellette-Kuntz H, Coo H, Yu CT, Chudley AE, Noonan A, Breitenbach M, et al. Prevalence of pervasive developmental disorders in two Canadian provinces. J Pol Pract Intellectual Disabilities 2006;3(3):164-72.

(20.) The Senate Standing Committee on Social Affairs, Science and Technology. Final Report on the enquiry on the funding for the treatment of autism. Pay now or pay later. Autism families in crisis, 2007. Available online at: http://www.parl.gc.ca/39/1/parlbus/commbus/senate/com-e/ soci-e/repe/repfinmar07-e.htm#_Toc162403105 (Accessed November 6, 2007).

(21.) Mandell DS, Novak MM, Zubritsky CD. Factors associated with age of diagnosis among children with autism spectrum disorders. Pediatrics 2005;116:1480-86.

(22.) Library of Parliament. Provincial and territorial funding programs for autism therapy, 2006. Available online at: http://www.parl.gc.ca/ information/library/PRBpubs/prb0622-e.htm (Accessed May 5, 2008).

Helene M.J. Ouellette-Kuntz, MSc, [1] Helen Coo, MSc, [2] Miu Lam, PhD, [1] C.T. Yu, PhD, [3] Marlene M. Breitenbach, MSEd, [4] Paula E. Hennessey, BA, [5] Jeanette J.A. Holden, PhD, [6] Hilary K. Brown, BA, [7] Andrea L. Noonan, MA, [8] Robert B. Gauthier, MEd, MSc, [9] Lori R. Crews, MSEd [9]

Author Affiliations

[1.] Associate Professor, Department of Community Health and Epidemiology, Queen's University, Kingston, ON

[2.] Research Associate, Department of Community Health and Epidemiology, Queen's University, Kingston, ON

[3.] Associate Professor, Department of Psychology, University of Manitoba, Winnipeg, MB

[4.] Special Education Autism Coordinator, Department of Education and Early Childhood Development, Charlottetown, PE

[5.] Provincial Consultant, Intervention Services & Autism, Department of Health & Community Services, St. John's, NL

[6.] Professor, Department of Psychiatry, Queen's University, Kingston, ON

[7.] Research Assistant, Department of Community Health and Epidemiology, Queen's University, Kingston, ON

[8.] Early Intervention Coordinator, Department of Social Services and Seniors, Charlottetown, PE

[9.] Professional Development Consultant, Department of Education, St. John's, NL

Correspondence and reprint requests: Prof. Helene Ouellette-Kuntz, Department of Community Health and Epidemiology, Queen's University, 191 Portsmouth Avenue, Kingston, ON K7M 8A6, Tel: [phone], Fax: [phone], E-mail: [e-mail]

Table 1. Agencies in Manitoba, Southeastern Ontario, Prince Edward
Island and Newfoundland and Labrador that Identify Children with an
Autism Spectrum Disorder for the National Epidemiologic Database
for the Study of Autism in Canada

Region           Agency                     Population Served

Manitoba         Children's Special         All children under
                 Services, Manitoba           the age of 18,
                 Department of                with the exception
                 Family Services &            of children living
                 Housing                      on reserves

Southeastern     Limestone District         School-age children
Ontario            School Board

                 Upper Canada District      School-age children
                   School Board

                 Hastings & Prince          School-age children
                   Edward District
                   School Board

                 Algonquin &                School-age children
                   Lakeshore Catholic
                   District School
                   Board

                 Catholic District          School-age children
                   School Board of
                   Eastern Ontario

                 Conseil des ecoles         School-age children
                   publiques de
                   l'Est de l'Ontario

                 Conseil des ecoles         School-age children
                   catholiques de
                   langue francaise
                   du Centre-Est

                 Child Development          All children under
                   Centre, Hotel              18 years of age
                   Dieu Hospital *            living in
                                              Southeastern Ontario

                 Pathways for               Children 2-5 years
                   Children & Youth,          of age who have
                   Autism Intervention        been diagnosed
                   Program                    or are considered
                                              end of the autism
                                              spectrum

Prince Edward    Department of              Pre-school and
Island             Education and Early        school-age children
                   Childhood Development

Newfoundland &   Department of Education    School-age children
Labrador
                 Department of Health and   Children 18-84 months
                   Community Services,        of age with an autism
                   Early Intensive            spectrum disorder
                   Intervention Services

Region           Method of Data             Year Data
                   Collection                 Collection
                                              Started

Manitoba         Agency staff review        2002
                   files and complete
                   anonymized data
                   collection forms for
                   children under 18
                   years of age with an
                   autism spectrum
                   disorder

Southeastern     Agencies provide the       2003
Ontario            research team with
                   the date of birth
                   and sex of all
                   children under 15
                   years of age with
                   an autism spectrum
                   disorder, and send
                   information letters
                   and consent forms
                   to their parents
                   or legal guardians.
                   If a consent form is
                   sent back to the
                   study team, more
                   detailed demographic
                   and diagnostic
                   information is
                   collected by
                   telephone interview
                   with the parent or
                   legal guardian.

Prince Edward    Same as for                2002
Island             Southeastern
                   Ontario, except
                   includes all
                   children under
                   18 years of age
                   with an autism
                   spectrum disorder.

Newfoundland &   Same as for                2003
Labrador           Southeastern
                   Ontario

* Referral and assessment centre for children with suspected
developmental problems.

Table 2. Median Age at First Diagnosis of an Autism Spectrum Disorder
in Four Regions of Canada by Sex, Year of Initial Diagnosis and
Diagnostic Subtype

                                Manitoba

                                 n (%)            Median Age,
                                                     Months
                                                   (IQ Range)

Overall                       505 (100.0)         48.0 (30.0)
Sex
  Boys                         421 (83.4)         47.0 (29.5)
  Girls                        84 (16.6)          50.0 (37.5)

p-value for intra-regional
differences in median age
at diagnosis by sex                                  0.217

Year of initial diagnosis
  1997-1999                    87 (17.2)          49.0 (24.0)
  2000-2002                    177 (35.0)         46.0 (30.0)
  2003-2005                    241 (47.7)         48.0 (35.5)

p-value for intra-regional
differences in median age
at diagnosis by year of
initial diagnosis                                    0.562

Diagnostic subtype
  Autistic disorder            183 (36.2)         42.0 (19.0)
  PDD-NOS                      69 (13.7)          77.0 (55.5)
  Asperger's disorder          59 (11.7)          101.0 (65.0)
  ASD                          194 (38.4)         42.0 (20.3)

p-value for intra-regional
differences in median age
at diagnosis by diagnostic
subtype                                              <0.001

                              Southeastern
                                Ontario

                                 n (%)            Median Age,
                                                     Months
                                                   (IQ Range)

Overall                        117(100.0)         55.0 (51.5)
Sex
  Boys                         99 (84.6)          53.0 (48.0)
  Girls                        18 (15.4)          64.0 (75.0)

p-value for intra-regional
differences in median age
at diagnosis by sex                                  0.255

Year of initial diagnosis
  1997-1999                    26 (22.2)          43.0 (24.5)
  2000-2002                    45 (38.5)          58.0 (55.5)
  2003-2005                    46 (39.3)          61.5 (53.5)

p-value for intra-regional
differences in median age
at diagnosis by year of
initial diagnosis                                    0.004

Diagnostic subtype
  Autistic disorder            24 (20.5)          34.0 (27.3)
  PDD-NOS                      25 (21.4)          59.0 (48.0)
  Asperger's disorder          29 (24.8)          89.0 (43.0)
  ASD                          39 (33.3)          47.0 (20.0)

p-value for intra-regional
differences in median age
at diagnosis by diagnostic
subtype                                              <0.001

                             Prince Edward
                                 Island

                                 n (%)            Median Age,
                                                     Months
                                                   (IQ Range)

Overall                        56 (100.0)         47.5 (41.0)
Sex
  Boys                         46 (82.1)          45.0 (42.0)
  Girls                        10 (17.9)          50.5 (72.3)

p-value for intra-regional
differences in median age
at diagnosis by sex                                  0.171

Year of initial diagnosis
  1997-1999                    18 (32.1)          46.5 (35.8)
  2000-2002                    17 (30.4)          49.0 (46.5)
  2003-2005                    21 (37.5)          46.0 (64.5)

p-value for intra-regional
differences in median age
at diagnosis by year of
initial diagnosis                                    0.205

Diagnostic subtype
  Autistic disorder            11 (19.6)          44.0 (23.0)
  PDD-NOS                      12 (21.4)          50.0 (41.8)
  Asperger's disorder           5 (8.9)           103.0 (40.5)
  ASD                          28 (50.0)          44.5 (24.5)

p-value for intra-regional
differences in median age
at diagnosis by diagnostic
subtype                                               0.02

                              Newfoundland
                               & Labrador

                                 n (%)            Median Age,
                                                     Months
                                                   (IQ Range)

Overall                        91 (100.0)         39.0 (17.0)
Sex
  Boys                         78 (85.7)          39.0 (17.3)
  Girls                        13 (14.3)          41.0 (18.0)

p-value for intra-regional
differences in median age
at diagnosis by sex                                  0.905

Year of initial diagnosis
  1997-1999                    22 (24.2)          42.0 (17.3)
  2000-2002                    47 (51.6)          37.0 (24.0)
  2003-2005                    22 (24.2)          42.0 (14.5)

p-value for intra-regional
differences in median age
at diagnosis by year of
initial diagnosis                                    0.745

Diagnostic subtype
  Autistic disorder            27 (29.7)          40.0 (18.0)
  PDD-NOS                     19 (20.9) *     48.0 (33.0) ([dagger])
  Asperger's disorder              -                   -
  ASD                          45 (49.5)          36.0 (13.5)

p-value for intra-regional
differences in median age
at diagnosis by diagnostic
subtype                                              0.036

                              p-value for
                             Inter-regional
                             Differences in
                               Median Age
                              at Diagnosis

Overall                          <0.001
Sex
  Boys                           <0.001
  Girls                          0.067

p-value for intra-regional
differences in median age
at diagnosis by sex

Year of initial diagnosis
  1997-1999                       0.12
  2000-2002                      0.007
  2003-2005                      0.002

p-value for intra-regional
differences in median age
at diagnosis by year of
initial diagnosis

Diagnostic subtype
  Autistic disorder              0.206
  PDD-NOS                        0.001
  Asperger's disorder            0.603
  ASD                            0.005

p-value for intra-regional
differences in median age
at diagnosis by diagnostic
subtype

Notes: The n denotes sample size used in the analysis, and does
not reflect the total number of children diagnosed with an
autism spectrum disorder for any of the categories listed.
Percents are based on intra-regional totals. IQ = Interquartile,
PDD-NOS = Pervasive developmental disorder, not otherwise specified,
ASD = Autism spectrum disorder (non-specific diagnosis).

* Due to small numbers, the Asperger's disorder and PDD-NOS
categories were grouped together.

([dagger]) Values are for PDD-NOS only.

Table 3. Median Age at First Diagnosis of an Autism Spectrum Disorder
in Manitoba by Year of Diagnosis and Diagnostic Subtype

Diagnostic                    Year of Initial Diagnosis of
  Subtype                     an Autism Spectrum Disorder

                               1997-1999

                        n     Median Age,
                              Months (IQ
                                 Range)

Autistic disorder      28     44.0 (19.5)
PDD-NOS                20     56.5 (47.8)
Asperger's disorder     5     70.0 (54.0)
ASD                    34     43.5 (24.8)

Diagnostic                    Year of Initial Diagnosis of
  Subtype                     an Autism Spectrum Disorder

                               2000-2002

                        n     Median Age,
                              Months (IQ
                                 Range)

Autistic disorder      58     39.5 (15.5)
PDD-NOS                20     75.0 (61.5)
Asperger's disorder    23     74.0 (58.0)
ASD                    76     43.0 (18.3)

Diagnostic                    Year of Initial Diagnosis of
  Subtype                     an Autism Spectrum Disorder

                               2003-2005

                        n     Median Age,
                              Months (IQ
                                 Range)

Autistic disorder      97     42.0 (20.0)
PDD-NOS                29     92.0 (51.5)
Asperger's disorder    31     108.0 (59.0)
ASD                    84     41.0 (19.3)

Diagnostic            p-value
  Subtype

Autistic disorder     0.651
PDD-NOS               0.021
Asperger's disorder   0.080
ASD                   0.391

Notes: The n denotes sample size used in the analysis, and does not
reflect the total number of children diagnosed with an autism
spectrum disorder for any of the categories listed.

IQ = Interquartile, PDD-NOS = Pervasive developmental disorder,
not otherwise specified, ASD = Autism spectrum disorder
(non-specific diagnosis).