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Comparative Study
. 2017 May 9;7(5):e015549.
doi: 10.1136/bmjopen-2016-015549.

Autism spectrum disorder: updated prevalence and comparison of two birth cohorts in a nationally representative Australian sample

Tamara May  1   2 , Emma Sciberras  2   3 , Amanda Brignell  1   2 , Katrina Williams  1   2   4
Affiliations
Comparative Study

Autism spectrum disorder: updated prevalence and comparison of two birth cohorts in a nationally representative Australian sample

Tamara May et al. BMJ Open. .

Abstract

Objectives: This study aimed to (1) provide an update on the prevalence of parent-reported autism spectrum disorder (ASD) diagnosis and new information about teacher-reported ASD in two nationally representative Australian cohorts at ages 10-11 years, (2) examine differences in cohort demographic and clinical profiles and (3) compare the prevalence of teacher-reported ASD and any changes in categorisation over time across the cohorts.

Design: Secondary analyses were undertaken using data from the Longitudinal Study of Australian Children (LSAC).

Participants: Children were recruited at kindergarten age (K cohort; birth year 1999/2000) and birth (B cohort; birth year 2003/2004), with follow-up of every 2 years for six waves.

Primary outcome measures: Parent-reported and teacher-reported ASD diagnosis was ascertained at three time points (waves 4-6).

Results: At age 10-11 years, the adjusted prevalence of parent-reported ASD diagnosis was 3.9% (95% CI 3.2 to 4.5) and 2.4% (95% CI 1.6 to 2.9) in the B and K cohorts, respectively. Teacher-reported prevalence of ASD was 1.7% (95% CI 1.2 to 2.1) in the B cohort and 0.9% (95% CI 0.56 to 1.14) in the K cohort. Parents reported fewer conduct and peer problems and teachers more pro-social behaviour in B relative to K cohort ASD children. Children reported only by parents in the later-born B cohort had milder behaviour problems than parent-agreed and teacher-agreed cases. Although individual switching to ASD from other categories from 8-9 to 10-11 years was low (K cohort n=5, B cohort n=6), teachers reported more children with ASD in the B than K cohort at 10-11 years and fewer children with emotional/ behavioural problems.

Conclusions: The higher prevalence of parent-reported and teacher-reported ASD diagnosis in the later-born cohort may be partially explained by identifying children with milder behavioural problems as ASD and a change in the use of diagnostic categories in schools.

Keywords: Autism Spectrum Disorder; epidemiology; prevalence.

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Conflict of interest statement

Competing interests: None declared.

Figures

Figure 1
Figure 1
Adjusted prevalence of ASD according to teacher and parent report in the birth (B) and kindergarten (K) cohorts with 95% CI.
Figure 2
Figure 2
Frequency of age of diagnosis in the birth (B) and kindergarten (K) cohorts according to parent report at 10–11 years.
Figure 3
Figure 3
Adjusted teacher-reported percentages of students requiring special assistance in school in the birth (B) and kindergarten (K) cohorts at 10–11 years of age.
See this image and copyright information in PMC

References

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