. 2018 Nov 5;9:52. doi: 10.1186/s13229-018-0235-3

Table 1.

Inclusion criteria, recruitment and collection methods of the samples from UK, Japan and India

	UK	Japan	India
Inclusion criteria	All Aged 4–9 years Lives in UK No diagnosed ID No siblings in the study	All Aged 4–9 years Lives in Tokyo No diagnosed ID No siblings in the study	All Aged 4–9 years Lives in Kolkata or Delhi No diagnosed ID Primary language Hindi (if in Delhi) or Bengali (if in Kolkata) No visual, hearing, motor, neurological or mental health disorder No siblings in the study
	Cases Diagnosed by recognised clinical service, according to DSM-IV^a or DSM-5^b criteria.	Cases Diagnosis confirmed by school and/or clinic Diagnosis by DSM-IV^a/ICD-10^c No additional diagnosis other than ASD	Cases Diagnosis by DSM-IV^a/ICD-10^c
	Controls No neurodevelopmental disorder	Controls No diagnosable condition	Controls No formal diagnosis of any mental health condition
Autism recruitment	Via ARC’s volunteer database	Special education schools for children with developmental disorders	Not-for-profit organisations providing support for people with ASD
Control recruitment	Mainstream schools in Cambridgeshire, UK	Mainstream schools in Tokyo	Mainstream schools in Kolkata and Delhi, general population
AQ-Child method of completion	Cases online; controls pen and paper	Pen and paper	Pen and paper
Informant	Either parent	Mothers	Either parent

ARC Autism Research Centre, University of Cambridge, DSM Diagnostic and Statistical Manual of Mental Disorders, ICD International Statistical Classification of Diseases and Related Health Problems, UK United Kingdom

^aDSM-IV [48]

^bDSM-5 [1]

^cICD-10 [49]