Table 2.

Operational research definitions of ASD based on DSM-IV-TR^a criteria

	ASD-RIc	ASD-RNd
Total # of criteria metb	≥3	≥6
Minimum # of criteria met from each of 3 categoriesb:
Social interaction	at least 2	at least 2
Communication	at least 1	at least 1
	or	and
Restricted, repetitive behavior	at least 1	at least 1
Exclusionary diagnosese:	CDD Rett’s disorder	CDD Rett’s disorder

Abbreviations: ASD: Autism spectrum disorder; ASD-R_I: Research-defined ASD, inclusive criteria; ASD-R_N: Research-defined ASD, narrow criteria; CDD: Childhood disintegrative disorder.

^aDue to retrospective nature of the data, which does not allow questioning the caregiver about the timing of symptom onset, the DSM-IV-TR age of onset (<3 years) criterion was not included.

^bCriteria determination is based on problems abstracted from medical and educational records, representing 58 groups of signs and symptoms of ASD that map to 12 distinct DSM-IV-TR criteria (4 social interaction, 4 communication, and 4 restricted, repetitive behavior) (Online Resource 3).

^cASD-R_I: The inclusive research definition of ASD (ASD-R_I), which encompasses the DSM-IV-TR autistic disorder (AD), Asperger’s disorder (AS), and pervasive developmental disorder not otherwise specified (PDDNOS) diagnostic categories, is based on the criteria for PDDNOS, which required “severe and pervasive impairment in the development of reciprocal social interaction associated with impairment in either verbal or nonverbal communication skills or with the presence of stereotyped behavior, interests, and activities…” (American Psychiatric Association, 2000). We operationalized “severe and pervasive impairment in the development of reciprocal social interaction” as meeting 2 of the 4 social interaction criteria (also required for AD and AS). Additionally, the definition requires meeting at least 1 of the communication criteria or 1 of the restricted, repetitive behavior criteria.

^dASD-R_N: A subset of individuals with ASD-R_I also meet stricter, more narrow research criteria (ASD-R_N) based on the DSM-IV-TR criteria for AD (a total of at least 6 criteria met, including at least 2/4 social interaction criteria, 1/4 communication criteria, and 1/4 restricted, repetitive behavior criteria).

^eExclusionary diagnoses were identified by diagnostic codes and confirmed by expert review of the records.