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Research Article                                                                                                                                        Open Access

## The Early Diagnosis of Preschool Children with Autism Spectrum Disorder in Norway: a Study of Diagnostic Age and Its Associated Factors

## Kenneth Larsen

Regional Resource Center for Autism, ADHD, Tourette Syndrome, and Narcolepsy, Oslo University Hospital, Norway

*Corresponding author: k\_larsen@mac.com

## Abstract

The early identification of autism spectrum disorder is important to ensure access to early intervention. Much research has focused  on  the  identification  of  early  behavioral  symptoms  and  screening.  This  study  examines  referral  for  diagnostic assessment, diagnostic age, and factors associated with diagnostic age for children with autism spectrum disorder. The results of this study indicate that children are referred and diagnosed later than they should be. Previous research has identified a valid time for the identification and diagnosis of this disorder as well as the diagnostic procedures and types of clinics that are associated with the appropriate diagnostic age.

Keywords: Diagnostic age; ASD; associated factors

Autism  spectrum  disorder  (ASD)  is  defined  by impairments in social interaction and social communication  as  well  as  restricted  and  repetitive patterns  of  behavior,  interests,  and  activities.  The symptoms are present from early childhood, and they impair or restrict an individual's daily functioning and participation (1,2).

The  early  identification  of  ASD  is  important  to reduce  parental  concern  and  stress  and  to  secure access  to  early  interventions  (3,4).  Recent  research has had promising results with the implementation of specially designed interventions for infants and toddlers with ASD (5-7). This research has emphasized the importance of identifying and diagnosing children with ASD at an early developmental stage.

Our knowledge of the early symptoms associated with the later  diagnosis  of  ASD  has  increased through focused research during recent decades. On the  basis  of  this  knowledge  of  early  behavioral symptoms related to the core areas of social interaction, social communication, and restricted and repetitive patterns of behavior, interests, and activities,  it  is  generally  accepted  that  children  with ASD may reliably be diagnosed as early as 24 months of  age  and,  for  certain  children,  no  later  than  36 months of age (4,8-10). However, this may not the case  for  all  affected  children,  especially  those  with less severe symptoms (11).

The actual mean diagnostic age for children with ASD is higher at approximately 48 months of age, and diagnosis sometimes occurs even later (12-15). Relevant  studies  of  diagnostic  age  are  outlined  in Table  1.  Several  factors  have  been  described  as affecting  the  diagnostic  age,  including  symptom severity,  regional  differences  between  and  within countries (16), level of parent concern, birth order, maternal education, siblings with ASD, development regression, and number of children in the family (1720). Gender has been proposed as another factor that influences early recognition, but no significant differences between girls and boys have been demonstrated  (21).  The  diagnostic  age  of  children with  ASD  in  Norway  is  not  currently  known. Knowledge  of  the  appropriate  diagnostic  age  and factors associated with the actual diagnostic age are important for the development of health care services and for the training of professionals in

TABLE 1. Relevant Studies of Age at Diagnosis of Autism Spectrum Disorder

| Study                                           | Region                                                     | Population (Age Group)                   | Diagnostic Age (Average in Months) *   | Factors Studied                                                                                                                           |
|-------------------------------------------------|------------------------------------------------------------|------------------------------------------|----------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------|
| Chakrabarti & Fombonne (2001)                   | England, Staffordshire                                     | Preschool children                       | AD                                     | 35 Referring source                                                                                                                       |
| Magnusson& Saemundsen (2001)                    | Iceland                                                    | 5 to 24 years old                        | Overall AD PDD-NOS                     | 41 43 to 49 † 5 †                                                                                                                         |
| Mandell et al. (2002)                           | US, Pennsylvania                                           | 3 to 16 years old                        |                                        | 76 to 95 Race                                                                                                                             |
| Lingam et al. (2003)                            | England, London                                            |                                          | AD AS                                  | 40 97                                                                                                                                     |
| Yeargin-Allsopp et al. (2003) Daley (2004)      | US, Atlanta India                                          | 3 to 10 years old 2.10 to 27.6 years old | PDD-NOS                                | 51 47 Demographic factors, cognitive functioning, source of identification 59 Specific symptoms, environmental factors, cultural factors, |
| Keen& Ward (2004) Chakrabarti & Fombonne (2005) | England, Doncaster England, Staffordshire India, New Delhi | 0 to 17 years old Preschool children     | AD                                     | socioeconomic factors 76 Educational placement                                                                                            |
| Juneja et al. (2005) Mandell et al. (2005)      | US, Pennsylvania                                           | 0 to 21 years old                        | AD AD                                  | 33 38 39 37 Living area (urban/rural), income, language level, specific symptoms,                                                         |
|                                                 |                                                            | 0 to 18 years old                        | AS PDD-NOS Overall                     | 45 39                                                                                                                                     |
| Goin-Kochel et al. (2006)                       | Several countries                                          | 1.7 to 22.1 years old                    | AD AS PDD-NOS                          | 41 90 50 Number of professionals visited, income                                                                                          |
| Wiggins et al. (2006)                           | US, Atlanta                                                | 8 years old                              | Overall AD AS PDD-NOS                  | 54 59 82 Gender, race/ethnicity, presence of Mental Retardation, degree of impairment                                                     |
|                                                 |                                                            |                                          |                                        | 65                                                                                                                                        |
| Latif & Williams (2007)                         | UK, South Wales                                            | 0 to 17 years old                        | ASD Overall AD AS ASD                  | 53 61 32 to 43 79 to 86 52 to 78                                                                                                          |
| Oslejskova et al.                               | Czech Republic, Brno                                       |                                          | Overall AD AS PDD-NOS Overall          | 66 to 71 74 129 81 82 Diagnostic subgroup                                                                                                 |
| (2007) Chen et al. (2008) Parner et al. (2008)  | Taiwan Denmark                                             |                                          | AD AD Overall AD AS                    | 45 to 46 Living area 56 to 61 64 to 71 Cohort                                                                                             |
| Williams et al.                                 | England, Avon                                              | 0 to 11 years old                        |                                        | 45 † 116 † Gender, maternal educational level                                                                                             |
| (2008)                                          |                                                            |                                          |                                        |                                                                                                                                           |
|                                                 |                                                            |                                          | PDD-NOS                                | 76 † 8 †                                                                                                                                  |
| Hertz-Picciotto & Delwiche (2009)               | US, California                                             | 0 to 9 years old                         | Overall AD                             | 58 to 63 Cohort 36 to 48 †                                                                                                                |
| Nassar et al. (2009)                            |                                                            | 0 to 8 years old                         |                                        |                                                                                                                                           |
|                                                 | Australia,                                                 |                                          |                                        |                                                                                                                                           |
|                                                 | Western                                                    |                                          |                                        |                                                                                                                                           |

Table continues next page

| Study                                             | Region                                                                                                     | Population (Age Group)   | Diagnostic Age (Average in Months) *   | Factors Studied                                                                                                                                                                                                                                                                                                                                                                                                      |
|---------------------------------------------------|------------------------------------------------------------------------------------------------------------|--------------------------|----------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Ouellette-Kuntz et al. (2009)                     | Canada, four regions                                                                                       | 2 to 18 years old        | AD AS PDD-NOS ASD                      | 33 to 44 † 89 to 103 † 48 to 77 † 36 to 47 † Gender, region, year of initial diagnosis, diagnostic subtype                                                                                                                                                                                                                                                                                                           |
| Perryman (2009)                                   | US, North Carolina                                                                                         |                          |                                        | 46 †                                                                                                                                                                                                                                                                                                                                                                                                                 |
| Shattuck et al. (2009)                            | US                                                                                                         |                          | AD ASD                                 | 88 † 106 † Gender, intelligence quotient, developmental regression, site                                                                                                                                                                                                                                                                                                                                             |
| Adelman (2010)                                    | US                                                                                                         | 0 to 11 years old        |                                        | 38                                                                                                                                                                                                                                                                                                                                                                                                                   |
| Mandell et al. (2010)                             | US                                                                                                         | 0 to 10 years old        | AD ASD Overall                         | 59 to 66 61 to 73 65                                                                                                                                                                                                                                                                                                                                                                                                 |
| Noterdaeme & Hutzelmeyer-Nickels (2010)           | Germany, Munich                                                                                            |                          | AD AS                                  | 76 110                                                                                                                                                                                                                                                                                                                                                                                                               |
| Chamak et al. (2011) Fountain et al. (2011)       | France US, California                                                                                      | 4 to 45 years old        | AD                                     | 20 to 120 43 to 60 †                                                                                                                                                                                                                                                                                                                                                                                                 |
| Kalkbrenner et al. (2011) Rosenberg et al. (2011) | US                                                                                                         | 0 to 18 years old        |                                        | 57                                                                                                                                                                                                                                                                                                                                                                                                                   |
|                                                   | US, North Carolina                                                                                         | 0 to 8 years old         | AD AS PDD-NOS ASD Overall              | 38 88 45 42 48                                                                                                                                                                                                                                                                                                                                                                                                       |
| Coo et al. (2012)                                 | Canada                                                                                                     | 1 to 14 years old        | AD AS PDD-NOS ASD Overall              | 58 94 69 54 61 Diagnostic subgroup, ethnocultural identity, being adopted, neighborhood median household income, urban/rural living area, gender, year of initial diagnosis, birthplace, siblings with ASD                                                                                                                                                                                                           |
| Valicenti-McDermott et al. (2012)                 | US, University-affiliated developmental center, The Children´s Evaluation and Rehabilitation Center (CERC) | 1 to 6 years old         |                                        | 38 Ethnicity, maternal education level                                                                                                                                                                                                                                                                                                                                                                               |
| Frenette et al. (2013)                            | Canada, Nova Scotia                                                                                        | 0 to 15 years old        |                                        | 55 †                                                                                                                                                                                                                                                                                                                                                                                                                 |
| Mishaal et al. (2014)                             | Israel                                                                                                     | 15 to 72 months old      |                                        | 28 Gender, first-born status, sibling with ASD, developmental regression, parental age, parental education, Autism Diagnostic Observation Schedule severity score, Autism Diagnostic Interview, Revised, score, Vineland Adaptive Behavior Scales (VABS) composite score 64 Cohort effects, parental education, ethnicity, intellectual ability, symptom severity, communications skills, social skills, psychiatric |
| Mazurek et al. (2014)                             | US, Autism Speaks Autism Treatment Network (AS-ATN)                                                        | 2.0 to 17.6 years old    |                                        | symptoms                                                                                                                                                                                                                                                                                                                                                                                                             |
|                                                   |                                                                                                            |                          |                                        | 35 114 Gender, birth order, cognitive functioning, language level, adaptive level, insurance coverage, maternal education, sibling or family                                                                                                                                                                                                                                                                         |
| Bickel et al. (2015)                              | US, Boston                                                                                                 | Children                 | ASD, PDD-NOS AS                        | member with ASD, number of children in the house                                                                                                                                                                                                                                                                                                                                                                     |
| Jo et al. (2015)                                  | US                                                                                                         | 3 to 17 years old        |                                        | 28 to 76 Ethnicity, symptom severity, family structure, co-occurring health conditions                                                                                                                                                                                                                                                                                                                               |

AD, Autistic Disorder; AS, Asperger Syndrome; ASD, autism spectrum disorder; PDD-NOS, pervasive developmental disorder, not otherwise specified; US, United States primary  health  care  settings  and  clinics  in  which children are diagnosed with ASD.

Diagnostic assessment for ASD is a comprehensive interdisciplinary procedure that requires thorough knowledge of both child development and the core areas of ASD. International practice parameters for the assessment and diagnosis of ASD  in children have been published  (22).  In  Norway,  the  Regional  Resource Center  for  Autism,  ADHD,  Tourette's  Syndrome, and Narcolepsy has published regional practice parameters for the assessment and diagnosis of ASD in children, adolescents,  and  adults (23).  These parameters  state  that  diagnostic  assessment  should include a medical examination; an evaluation of the child's  developmental  and  medical  history;  and  an assessment  of  the  child's  social  interaction,  social communication, language skills, restricted and repetitive  behaviors,  cognitive  level,  and  adaptive behaviors.  It  is  recommended  that  most  of  the assessment should be based on standardized instruments, including the Autism Diagnostic Observation  Schedule  and  the  Autism  Diagnostic Interview,  Revised.  Whether  diagnostic  assessment procedures influence the diagnostic age is not known. Different aspects of the diagnostic assessment  may  influence  diagnostic  age,  including the  type  of  clinic  and  the  use  of  standardized assessment tools.  Research has found  that the diagnostic procedures that differ from clinic to clinic can influence diagnostic conclusions (16), especially with regard to subgrouping within the autism spectrum.

Norwegian  legislation  gives  every  child  who  is more than 12 months old the individual right to a place  in  a  day  care  center.  Eighty  percent  of  all children between the ages of 1 and 2 years regularly attend day care centers, and this number rises to 97% for 3- to 5-year-old children. The staff members of day  care  centers  may  have  bachelor's  degrees  in childhood education or college degrees in childhood care, or they may  have no education beyond mandatory  schooling.  Norwegian  day  care  centers and  preschools  focus  on  play  and  do  not  include traditional classroom activities or settings. All Norwegian  children have access to health and developmental  checks  at  community  health  care centers, and they are invited at regular intervals for short follow-up visits. Primary care doctors are free of  charge  for  all  children  who  are  16  years  old  or younger, and each child has a regular primary care physician.  A  referral  from  this  doctor  or  from  a community health clinic or child welfare services is required  for  diagnostic  assessment  at  a  specialist clinic.

In accordance with Norwegian law, the diagnostic assessment and official diagnosis of ASD must occur at  a  specialized  clinic  that  has  been  organized  at  a hospital.  Children  who  are  referred  to  specialist clinics with symptoms of ASD are entitled to health services within a predefined time frame. For children between the ages of 0 and 2 years, health services for ASD assessment should be provided within 4 weeks of  recognition  of  need.  The  corresponding  time frame for children between the ages of 3 and 6 years is 6 weeks. There are two main types of clinics that perform the diagnostic assessment of children with ASD:  habilitation  clinics  and  child  and  adolescent mental health clinics. Habilitation clinics are typically staffed with pediatricians, child neurologists, psychologists, special educators, social nurses, physiotherapists,  and  others.  Child  and  adolescent mental health clinics are typically staffed with child psychiatrists, psychologists, special educators, social nurses,  and  others.  How  such  differences  in  the professions  represented  in  these  clinics  may  affect diagnostic procedure and age are not known.

The southeastern part of Norway has a population of 2.8 million, and Norway has a total population of 5 million. Southeastern Norway has a higher density of inhabitants than most other regions  in Norway, and  it includes both  rural and  city areas.  The prevalence of ASD in Norway is estimated at 51 to 60 individuals per 10,000 population (24,25).

This  study  had  two  main  goals.  First,  the  study investigated the following hypotheses: (1) Preschool children with ASD are diagnosed at the same age in Norway as in other Western countries; and (2) The diagnostic process for preschool children with ASD is  standardized  and  uniform.  Second,  this  study sought to explore factors that may be associated with diagnostic age.

## Methods Participants

Participants  in  this  study  were  recruited  from  the records of special health clinics in the southeastern part of Norway.  Sixteen specialist clinics were identified, and 15 consented to patient recruitment. Seven of these clinics were a part of a general child and adolescent mental health trust, and eight  were habilitation clinics. The  15  clinics revealed  114 preschool  children  who  had  been  diagnosed  with ASD during the 2011 calendar year: 78 with autistic disorder,  28  with  atypical  autism,  2  with  Asperger syndrome,  and  11  with  pervasive  developmental disorder not otherwise specified. This comprises all of  the  children  who  were  diagnosed  with  ASD  at these clinics.

Each hospital includes several mental health clinics. For the purpose of analysis, the mental health clinics were grouped together according to hospital.

## Measures

All  clinics  completed a  questionnaire developed by the author for each child diagnosed with ASD during 2011.  The  questionnaire  was  developed  to  assess relevant information regarding diagnostic assessment and  the  age  at  diagnosis.  The  questionnaire  first assessed demographic information about each child. It was also used to collect information about how the diagnostic  assessment  had  been  conducted,  mainly by assessing the standardized diagnostic assessment tools used in each case. The selection of diagnostic assessment tools included in the questionnaire was based on the instruments mentioned in the Regional Practice Parameters for the assessment and diagnosis of ASD. The final diagnostic decision and the child's age  at  diagnosis  are  assessed  by  the  questionnaire. The specific questions asked are detailed in Table 2.

TABLE 2. Elements of the Questionnaire

| Demographic Information                                            | Demographic Information                                            |
|--------------------------------------------------------------------|--------------------------------------------------------------------|
| Specialist clinic                                                  | Specialist clinic                                                  |
| Sex                                                                | Sex                                                                |
| Ethnicity                                                          | Ethnicity                                                          |
| Municipality                                                       | Municipality                                                       |
| Age at referral                                                    | Age at referral                                                    |
| Referring agency                                                   | Referring agency                                                   |
| Diagnostic Process                                                 | Diagnostic Process                                                 |
| Diagnostic Tools                                                   | Diagnostic Tools                                                   |
| Social interaction, communication and language, and restricted and | Social interaction, communication and language, and restricted and |
| repetitive behaviors                                               | repetitive behaviors                                               |
|                                                                    | Autism Diagnostic Observation Schedule (ADOS)                      |
|                                                                    | Autism Diagnostic Interview, Revised (ADI-R)                       |
|                                                                    | Social Communication Questionnaire (SCQ)                           |
|                                                                    | Diagnostic Scale for Social andCommunicationDisorders (DISCO)      |
|                                                                    | Childhood Asperger Syndrome Test (CAST)                            |
|                                                                    | Modified Checklist for Autism in Toddlers (M-CHAT)                 |
| Cognitive assessment                                               | Cognitive assessment                                               |
|                                                                    | Wechsler Intelligence Scales (WPPSI-R/WPPSI-III)                   |
|                                                                    | Leiter International Performance Scale, Revised (Leiter-R)         |
|                                                                    | Bayley Scales of Infant and Toddler Development (Bayley)           |
|                                                                    | Mullen Scales of Early Learning (Mullen)                           |
|                                                                    | Psychoeducational Profile (PEP-3)                                  |
|                                                                    | Behavior Rating of Executive Functioning (BRIEF)                   |
| Language assessment                                                | Language assessment                                                |
|                                                                    | Språk (6-16)                                                       |
|                                                                    | Tidlig Registrering Av Språkutvikling (TRAS)                       |
|                                                                    | Reynell Developmental Language Scales (Reynell)                    |
|                                                                    | Children's Communication Checklist II (CCC-2)                      |
|                                                                    | British Picture Vocabulary Test (BPVS)                             |
| Adaptive assessment                                                | Adaptive assessment                                                |
|                                                                    | Vineland Adaptive Behavior Scales (VABS)                           |
| Other assessments                                                  | Other assessments                                                  |
|                                                                    | Achenbach System of Empirically Based Assessment (ASEBA)           |
|                                                                    | Aberrant Behavior Checklist (ABC)                                  |
|                                                                    | The Strengths and Difficulties Questionnaire (SDQ)                 |
|                                                                    | Developmental Behavior Checklist (DBC)                             |
| Diagnosis                                                          | Diagnosis                                                          |
| Diagnostic age                                                     | Diagnostic age                                                     |

The  professionals  involved  in  the  provision  of assessment  services  completed  the  questionnaires; this included pediatricians, psychologists, and social workers. The data for each participant were retrieved from each clinic's  electronic  patient  journal  by  the local professional and then transferred to the questionnaire developed for this study.

Demographic information about the participants is presented in Table 3.

TABLE 3. Demographic Information

| Participants (n = 115)         |   Participants (n = 115) |
|--------------------------------|--------------------------|
| Gender                         |                          |
| Male                           |                       95 |
| Female                         |                       19 |
| Ethnicity                      |                          |
| European                       |                       78 |
| Asian                          |                       15 |
| African                        |                       16 |
| Mixed                          |                        5 |
| Referring Agency               |                          |
| General practitioner           |                       57 |
| Community health center        |                       19 |
| Children's ward at hospital    |                       17 |
| Child welfare service          |                        8 |
| Specialist pedagogical service |                        3 |
| Other                          |                       10 |

## Statistical Analysis

The results are presented on the basis of descriptive statistics for the participants. To explore the possible factors  that  may  affect  the  diagnostic  age  of  the participants in this study, one-way analysis of variance was used for nominal variables; regression was  used  for  all  other  variables.  All  analysis  was conducted with the use of SPSS software, version 22.

## Results Diagnostic Age

The diagnostic age was reported for each individual child and is defined as the child's age in months at diagnosis.  The  mean  diagnostic  age  of  preschool children  with  ASD  was  46.4  months  (standard deviation, 13.5 months). The range of diagnostic age was  13  to  75  months,  and  the  median  age  was  45 months. A minority of 3.5% of the children (n = 4) was diagnosed before or at 24 months of age, and 27.2% of the children (n = 31) were diagnosed before or at 36 months of age.

## Diagnostic Assessment Procedure

The use of standardized diagnostic assessment tools varied among participants, and the frequencies and percentages  of  cases  for  which  each  diagnostic assessment tool was used are listed in Table 4. The diagnostic assessment tools used did not vary significantly  on the basis of whether diagnosis occurred  in  a  mental  health  clinic  or  a  habilitation clinic.

TABLE 4. Frequency of Use of Diagnostic Assessment Tools (n=115)

| Diagnostic Assessment Tool   |   Frequency of Use |   Percentage of Cases |
|------------------------------|--------------------|-----------------------|
| ADOS                         |                106 |                  99.2 |
| ADI-R                        |                 97 |                  84.3 |
| Others*                      |                 68 |                  59.1 |
| VABS                         |                 37 |                  32.2 |
| Bayley                       |                 31 |                  27.0 |
| WPPSI-R/WPPSI-III            |                 21 |                  18.3 |
| ASEBA                        |                  8 |                   7.0 |
| Mullen                       |                  7 |                   6.1 |
| SCQ                          |                  6 |                   5.2 |
| Reynell                      |                  6 |                   5.2 |
| Leiter-R                     |                  5 |                   4.3 |
| BPVS                         |                  4 |                   3.5 |
| PEP-3                        |                  3 |                   2.6 |
| M-CHAT                       |                  2 |                   1.7 |
| CAST                         |                  1 |                   0.9 |
| BRIEF                        |                  1 |                   0.9 |

*This category consists of unpublished checklists and diagnostic tools that do not measure social, communication, or behavioral symptoms

TABLE 5. Statistics for Each Clinic Included in the Present Study

| Clinic No.   | Type of Clinic   |   Number of Children Diagnosed | Age at Referral in Months (Range)   | Age at Diagnosis in Months (Range)   |   Mean No. of Diagnostic Assessment Tools Used | Time From Referral to Diagnosis in Months (Range)   |   Number of Cases That Followed Published Guidelines |
|--------------|------------------|--------------------------------|-------------------------------------|--------------------------------------|------------------------------------------------|-----------------------------------------------------|------------------------------------------------------|
| Clinic 1     | Habilitation     |                             31 | 37 (8 to 68)                        | 42 (13 to 71)                        |                                           4.16 | 4 (1 to 9)                                          |                                                   22 |
| Clinic 2     | Habilitation     |                             13 | 40 (29 to 56)                       | 47 (33 to 68)                        |                                           3.77 | 7 (3 to 19)                                         |                                                    0 |
| Clinic 3     | Mental health    |                              3 | 38 (27 to 44)                       | 42 (31 to 48)                        |                                           3.00 | 4 (3 to 4)                                          |                                                    0 |
| Clinic 4     | Mental health    |                              1 | 45                                  | 55                                   |                                           3.00 | 10                                                  |                                                    0 |
| Clinic 5     | Mental health    |                              1 | 63                                  | 71                                   |                                           5.00 | 8                                                   |                                                    0 |
| Clinic 6     | Mental health    |                              3 | 57 (49 to 63)                       | 71 (68 to 75)                        |                                           5.33 | 14 (9 to 22)                                        |                                                    0 |
| Clinic 7     | Mental health    |                             14 | 46 (27 to 63)                       | 52 (33 to 68)                        |                                           2.79 | 6 (4 to 10)                                         |                                                    0 |
| Clinic 8     | Habilitation     |                              7 | 29 (14 to 45)                       | 38 (24 to 50)                        |                                           1.00 | 9 (3 to 32)                                         |                                                    0 |
| Clinic 9     | Habilitation     |                              4 | 40 (16 to 68)                       | 47 (29 to 68)                        |                                           2.75 | 5 (0 to 13)                                         |                                                    0 |
| Clinic 10    | Habilitation     |                              3 | 43 (26 to 54)                       | 46 (26 to 59)                        |                                           2.67 | 3 (0 to 5)                                          |                                                    0 |
| Clinic 11    | Habilitation     |                              3 | 34 (20 to 46)                       | 39 (26 to 54)                        |                                           6.20 | 6 (4 to 8)                                          |                                                    1 |
| Clinic 12    | Habilitation     |                              5 | 33 (23 to 42)                       | 40 (27 to 53)                        |                                           2.40 | 7 (4 to 11)                                         |                                                    0 |
| Clinic 13    | Mental health    |                             16 | 40 (11 to 56)                       | 49 (23 to 65)                        |                                           3.25 | 9 (3 to 28)                                         |                                                    0 |
| Clinic 14    | Mental health    |                              1 | 30                                  | 54                                   |                                           2.00 | 24                                                  |                                                    0 |
| Clinic 15    | Habilitation     |                              7 | 38 (25 to 48)                       | 52 (37 to 65)                        |                                           5.00 | 14 (1 to 36)                                        |                                                    2 |

The diagnostic assessment procedure included an average of 3.6 standardized assessment tools (range, 1 to 8). The most widely used tools were the Autism Diagnostic  Observation  Schedule  and  the  Autism Diagnostic Interview, Revised. The use of standardized assessment instruments is presented in Table 5. The number of standardized assessment tools used varied significantly ( p < .001) in accordance with the clinic that was conducting the diagnostic assessment.

Only  25  of  114  (21.7%)  diagnostic  assessments were  conducted  in  accordance  with  the  Regional Practice Parameters for the assessment and diagnosis of ASD, including the use of the Autism Diagnostic Observation  Schedule  and  the  Autism  Diagnostic Interview, Revised, as well as cognitive and adaptive assessment.  Only  three  clinics  reported  cases  in which the regional guidelines were used in a significant  proportion  of  the  assessments,  and  all three  of  these  were  habilitation  clinics.  No  clinics reported that they were following the guidelines in all cases. Children who were diagnosed on the basis of the regional guidelines had a mean diagnostic age of 38.5 months, whereas children who were diagnosed without  following these guidelines  had  a  mean diagnostic  age  of  48.7  months.  This  difference  in diagnostic age is statistically significant ( p = .001).

The  time  required to conduct  the diagnostic assessment was defined as the time from referral to a specialist clinic to the reported time of diagnosis. The mean time for all specialist  clinics  was  7.1  months (standard  deviation,  6.1  months;  range,  0  to  36 months).  The  exclusions  of  assessment  times  that were more than 12 months only slightly affected the mean time used (5.3 months). The mean diagnostic assessment time for each clinic varied from 3 months to  24  months, which reveals significant differences among the time used by each clinic. No significant difference was found between children diagnosed at a habilitation clinic and those diagnosed at a mental health clinic ( p = .197).

## Factors That Affect Diagnostic Age

Analysis  reveals that diagnostic age significantly varies  in  accordance  with  the  type  of  clinic  that conducted  the  diagnostic  assessment  ( p =  .048). Children who were diagnosed at child and adolescent mental health clinics had a mean diagnostic age of 56.3  months,  and  children  who  were  diagnosed  in habilitation clinics had a mean diagnostic age of 44.4 months. This difference in diagnostic age was found to be significant ( p = .023).

The age at referral is naturally correlated with the diagnostic age (r = 0.892; P <  .001).  There  are  no significant relationships between the age at referral and the time spent on the diagnostic assessment. The age at referral did not differ according to the agency that referred the child for assessment, except for the fact  that  children  who  are  referred  through  child welfare services are referred significantly later. Analysis did not reveal significant differences in age at referral or at final diagnosis. No other associations related to age at referral were examined.

Diagnostic  age  did  not  differ  significantly  by gender  ( p =  .214),  and  ethnicity  did  not  influence either age at referral ( p = .132) or age at diagnosis ( p = .13).

The International Statistical Classification of Diseases and Related Health Problems, 10th Revision diagnostic subgroup was associated with age at referral and thus also diagnostic age, although not with regard to the time spent on the diagnostic assessment. Children in subgroups  F84.5  (Asperger  syndrome)  and  F84.9 (Pervasive developmental disorder, unspecified) were  later  referred  for  diagnostic  assessment  at  a significant rate as compared with children in subgroup  F84.1  (Atypical  autism)  ( p =  .048  and p =  .022,  respectively).  Other  significant  differences were not found among diagnostic subgroups.

## Discussion

The  current  study  examined  the  diagnostic  age  of preschool-aged children with ASD. The results show that most of these children in the southeastern region of  Norway  are  diagnosed  at  a  mean  age  of  46.4 months.  This  is  in  line  with  other  international studies (8,17,26-27), and it is considerably later than research has indicated it possible (4, 15). The study also  explored  the  possible  factors  that  affect  the diagnostic age of children with ASD.

The diagnostic age varied significantly in accordance  with  the  type  of  clinic  to  which  the children were referred. The diagnostic procedure also varied among the different clinics that participated in this  study.  These  results  add  information  to  the existing literature  to  suggest  that  there  are  regional and  between-clinic  differences  in  the  diagnosis  of ASD  (16,19).  The  current  study  also  shows  that children referred to habilitation clinics are diagnosed earlier than children referred to child and adolescent mental health clinics. Differences in the medical staff members  who  typically  provide  services  may  be  a factor that contributes to this difference. In addition, children with the most severe and typical symptoms of  ASD  are  traditionally  referred  to  habilitation clinics, and children with more  subtle features associated  with  ASD  are  traditionally  referred  to child  and  adolescent  mental  health  clinics.  The current study-like other studies before it (17,27)found  that  certain  subgroups  within  the  autism spectrum  were  associated  with  certain  diagnostic ages.  For  example,  children  in  subgroups  F84.5 (Asperger syndrome) and F84.9 (Pervasive developmental disorder, unspecified) were diagnosed later  that  children  in  subgroups  F84.0  (Childhood autism)  and F84.1 (Atypical  autism).  Children  with the  first  two  diagnoses  are  described  with  more subtle symptoms at a young age than children with the  later  diagnoses.  The  children  diagnosed  with Asperger  syndrome  and  Pervasive  developmental disorder, unspecified, were all diagnosed at child and adolescent mental health clinics. This strengthens the notion that children referred to mental health clinics often have more subtle symptoms.

The variations in diagnostic procedures and processes may pose a challenge to the national goals of equality in health services, especially because only 21.7% of diagnostic assessment were found to have been  conducted  in  accordance  with  the  regional practice parameters. This low number is still higher than that found when examining the use of standardized diagnostic instruments in other samples (19). Further investigations should examine barriers to  the  implementation  of  practice  parameters  and address how organizations may facilitate the use of practice  parameters  and  standardized  assessment instruments.

Previous  research  has  proposed  that  gender  and ethnicity may influence the diagnostic age of children with  ASD  (21,27).  However,  this  study  confirmed the findings of more recent research that there is no significant association between sex, ethnicity, and age at diagnosis (21). The primary health services being delivered  at  community  centers  and  by  physicians who  are  free  of  charge  may  contribute  to  more equality  across  ethnicities  than  has  been  found  in studies conducted in other countries.

One  important  factor  that  affects  the  diagnostic age of children with ASD is the age at referral to a specialist  clinic  for  formal  diagnostic  assessment. This study found that the age at referral did not differ significantly among the referring agencies, except for children  who  were  referred  through  child  welfare services.  Several  factors  may  contribute  to  the  late referral, including comorbid conditions and challenges as a result of parental reluctance (15,18,20,28). All referring agencies in  Norway observe children during consultations that last from 20 to 60 minutes, and there are often several months between such consultations. This system may contribute to the later diagnostic age of children with ASD in Norway. The identification  of  the  atypical development that is associated with ASD requires the systematic observation of behavioral patterns that are somewhat consistent across time and settings. This study  shows  that  most  children  with  ASD  are diagnosed at an older age than research indicates to be possible, and the system for referral in Norway may contribute  to  this  later  diagnosis.  Shifting  the detection  of  ASD  into  arenas  that  involve  the continuous  observation  of  a  child's  development (e.g., day care centers) may facilitate the identification and diagnosis of ASD at a younger age.

The time span from referral to a specialist clinic to actual diagnosis was found in this study to stretch out over  several  months.  This  time  span  may  not  be explained by extended use of standardized diagnostic instruments, and no significant association between the number of standardized diagnostic instruments and the length of the diagnostic assessment period was found. For some children, the early identification of ASD may be required for effective early intervention.  Hence,  the  exploration  of  the  factors that contribute to the lengthy assessment period may be important to improve the provision of services to young children with ASD. Most diagnostic assessments of young children with possible ASD are conducted  in  outpatient  clinics.  This  may  lead  to diagnostic assessments that consist of one appointment  for  each  activity  that  makes  up  the diagnostic assessment. The organization of diagnostic assessments into single activities at different points in time may be driven by the system of economic reimbursement for Norwegian hospitals. The conduction of the diagnostic assessment via single assessment appointments may contribute  to  the  lengthy  time  span  of  diagnostic assessments  in  Norway.  Organizing  the  diagnostic assessment procedure in a manner that allows several observations, assessments, and examinations to occur  during  each  appointment  at  the  outpatient clinic  may  help  to  shorten  the  time  span  of  the diagnostic assessment.

According to Norwegian regulations, children are entitled  to  receive  certain  health  services  within  a predefined time frame. For children between the age of 0 and 2 years, health services should be provided within 4 weeks. The corresponding time frame for children between the ages of 3 and 6 years is 6 weeks. This time frame is most likely included in the time used on diagnostic assessment procedure, but according  to  Norwegian  authorities  it  should  be  a maximum waiting time.

This study has not collected information about the quality  of  the  diagnostic  classification  of  specific cases or clinics. No  information was collected regarding  the  reliability  of  standardized  assessment tools or final diagnostic conclusions.  The  only parameter  that  was  used  to  indicate  quality  in  this study was whether or not the regional guidelines were used.  The  results  indicate  that  children  who  are referred  to  clinics  in  accordance  with  the  regional guidelines are diagnosed at a younger age and thus may  indicate  the  quality  of  their  assessments  and close cooperation with referring agencies.

This  study  included  all  children  diagnosed  with ASD at the included clinics over the course of 1 year, and  information  from  the  official  records  of  each child was collected. Several factors still indicate that the results should be interpreted with caution. One year  is  a  relatively  short  period  for  data  collection, and the diagnostic age may lead to cohort effects not being adjusted for appropriately. Only children who are younger than school age (i.e., those <6 to 7 years old) were included in the study, so children who were diagnosed later may be missed. This indicates that the actual mean diagnostic age may be even higher than that  found  in  this  study.  This  study  also  did  not collect information about comorbidities, which may influence  the  diagnostic  assessment  procedure,  the time spent on diagnostic assessment, and the diagnostic age.

Children  with  ASD  make  up  a  heterogeneous group that differs widely with regard to the diversity and severity of symptoms. For some children with ASD,  the  symptoms  of  the  impairment  do  not become relevant or apparent when they are young, and a formal diagnosis will not be relevant during the early  years.  It  may  not  be  possible  or  necessary  to diagnose all children with ASD when they are 3 years old or younger.

## Clinical Significance

Norwegian  children  with  ASD  are  identified  and diagnosed  considerably  later  than  the  age  research has  indicated  to  be  optimal  for  reliable  and  valid diagnosis. Differences in diagnostic procedures and clinic types seem to be associated with diagnostic age. The procedures for referral and the agencies responsible for referral to diagnostic assessment may also contribute to a later diagnostic age.

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