Autism epidemiology: distinguishing between identification and prevalence

Autism (referred to as ‘autism spectrum disorder’ in the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders) is a lifelong neurodevelopmental condition, characterised by difficulties in social communication and social interaction, and restricted, repetitive behaviours, interests or activities.1 Prevalence refers to the proportion of individuals in a population who have a specific condition or characteristic at a specific time (point prevalence) or time period (period prevalence).2 Reliably estimating autism prevalence is essential to estimate need and allocation of health and social care resources. Similarly, identifying autism on an individual level is important, as late-diagnosed autistic persons describe receiving their diagnosis as life-changing, enabling access to valuable forms of support.3 This article discusses different approaches to case ascertainment employed in autism prevalence studies, and their merits and disadvantages. Though this paper pertains to autism epidemiology, it is important to acknowledge that many of the underlying principles were developed outside of autism research.