Table 2.

Characteristics associated with age at autism spectrum disorder diagnosis.^a

Characteristic	Earlier diagnosis	Later diagnosis	No relationship
Clinical characteristics
Symptoms	More symptoms/greater level of impairment [15, 27, and 29]	Higher communication skills [36]	Repetitive and unacceptable social behavior [36]
	Developmental regression [28 and 39] and higher social function [36]
	Toe walking [13 and 42]	Oversensitivity to pain [13]	Not responding to name when called, self-injury, aggressive to others, insistence on sameness, echolalia, and spins self [13]
	Language deficits, sustained odd play, and hand flapping [13]		Language regression [42]
Cognition	IQ ≤ 70 versus >70 [28]	IQ ≥ 85 versus 50–84 [34]	Comorbid intellectual disability [36]
		Comorbid intellectual disability [39]	Intellectual disability [13, 15, and 37]
Comorbid conditions	Major congenital anomaly [37]	Previous classification of ASD and co-occurring psychiatric or neurologic disorders or symptoms [32]	Epilepsy and cerebral palsy [37]
		Hearing impairment [13]
		Attention-deficit/hyperactivity disorder [37]
Sociodemographic characteristics
Sex	Female [15]	Female [8, 14, and 28]	6, 9, 13, 19, 22, 26, 29, 33, 34, 36, 37, 39, and 41
Race/ethnicity	White versus all other racial groups [6]	Non-White or Hispanic versus White [36]	Race [14, 13, 15, 27, and 30]
	Visible minority [41]	White versus all other racial/ethnic groups [33]	Ethnicity [13, 30, and 39]
		Other race and Hispanic ethnicity versus White [28]
		Black race [39]
		Hispanic and African-American versus White [42]
Socioeconomic status	Higher parental [14 and 36] or maternal [39] education	Living close to versus above poverty level [13]	Maternal education [22, 27, and 42]
	Higher family income [14]	Maternal education less than college versus college graduate [28]	Parent education or employment [29]
			Social status [34]
			Annual household income, parental education [30]
Other factors	Firstborn [12]	Being adopted [13]	Maternal age [28, 36, and 42]
	Older maternal age [37]	Medicaid eligibility due to disability versus other categories [33]	Birth order [29 and 42]
			Insurance type, parent age, and other children with ASD [29]
			Marital status, maternal mental illness, gestational age, and birth weight [37]
	Older siblings/family members with ASD [30, 41, and 42]	Born outside Canada [41]	Having health insurance [30]
		Mother born outside the United States and children whose deliveries were paid for by Medicaid [36]	Being adopted [41]
		Firstborn [36, 37, and 39]	Medicaid participation, bilingual household, and mother US-born [42]
Parental concern	Concern about social skills development and atypical behavior [29]	Attribution of symptoms to behavioral problems [27]
	Worry about initial symptoms [27]	Recognizing medical problem as first concern versus other behaviors [9]
		First concern about nonautism specific behavioral problems [30]
Systems interactions
Health care	Physician referral to a specialist [13]	Visiting a greater number of clinicians/professionals prior to diagnosis [9, 13, and 14]	Physician-conducted developmental testing in response to concern [13]
	Screening in response to concern [30]	Switching pediatricians in the first 5 years of life [30]
		Using health versus health and education records to assign a diagnosis [28]
Education	Diagnosis in a nonschool setting [15]	Placement in a nonautistic unit of school for learning difficulty versus mainstream school [10]	Use of standardized instrument to assign diagnosis [15]
	Referral from early intervention program versus physician office, school, or parent [29]	Using education records versus health and education records [28]
	Referral to early intervention [30]
Geographic region and associated characteristicsb
Region		Living outside northeastern United States [39]
		Living in the Midwest [30]
Urban/rural	Urban vs. suburban and rural [20]	Larger urban or rural county [33]	City versus rural versus suburban [29]
		Living in nonmetropolitan area [39]	Urban versus rural [41]
		Rural [13]
Community factors	Higher median property value [36]	Higher educated population [36]	Neighborhood median household income [41]
	Greater proportion of residents living in poverty [33 and 36]		Child psychiatrists nearby [36]
	Higher ASD prevalence [36]	Median income in second lowest versus lowest quartile, greater proportion of White residents second highest versus lowest quartile [39]	Per capita pediatricians or pediatric specialists, median income, percent residents on Medicaid, teacher student ratio, expenditures per student, percent non-English speaking students, and percent White residents [33]
	Greater number of neurologists of psychiatrists nearby, close proximity to a medical school [38]	Close proximity to a Treatment and Education of Autistic and Communication–related handicapped children program [38]	Greater number of primary care physicians nearby, close proximity to early intervention services, and living in a Health Professional Shortage Area [38]
State factors	Low state Child Health Insurance eligibility [33]	Median income in second lowest versus lowest quartile, greater proportion of White residents second highest versus lowest quartile [39]	Proportion of children 0–5 years in early intervention [33]
Cohort and period effects
Birth cohort		Older versus more recent [1, 2, 10, 11, 13, 14, 21, 24, 25, 30, 36, and 39]	Older versus more recent [5]
Period	Prior to versus after 2000 [39]	Earlier versus later [7, 18, 26, 33, and 35]	Earlier versus later [34]
		2005–2006 versus 1997–1999 [41]

ADDM: Automatic Database Diagnostic Monitor.

^aNumbers in parentheses reference included studies described in Table 1.

^bNot included here are specific differences across geographic region identified in the following studies: ADDM Network 2002 Principal Investigators, 2007; ADDM Network 2006 Principal Investigators, 2009; and ADDM Network 2008 Principal Investigators, 2012; Frenette et al. (2011); Howlin and Moore (1997); Ouellette-Kuntz et al. (2009); and Shattuck et al. (2009).