Reames, Emma; (2023) Estimating the Prevalence in Autism Spectrum Disorder Over Time: A Systematic Review and Meta-Analysis. Doctoral thesis (D.Clin.Psy), UCL (University College London).

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Abstract

Autism spectrum disorder (ASD) is a neurodevelopmental condition that has been increasing in prevalence across the globe since it was first recorded. This thesis addressed key questions regarding what the true prevalence of ASD is, how this has changed over time, and what factors might be contributing this. Part one is a conceptual introduction exploring how ASD is defined and diagnosed, and causal mechanisms that underly the condition. It then explored factors hypothesised to contribute to the observed rise in ASD, relating to both a true increase and an increase in discovery and diagnosis. How true versus diagnosed ASD can be determined is discussed. Part two is a systematic review and meta-analysis of 116 studies, tracking and charting changes in ASD prevalence over time, in relation to case ascertainment method and diagnostic criteria. It evidenced that there has been a rise in ASD over time, that methodological differences cannot account for a significant amount of the variability between prevalence estimates and that changes in diagnostic criteria are not sufficient to explain the observed increase in ASD. Part three is a critical appraisal of the research process, reflecting on the experience of the author in conducting a systematic review and meta-analysis in this field, along with the challenges, benefits and lessons learnt.

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