Factors Affecting Age at Initial Autism Spectrum Disorder Diagnosis in a National Survey

Table 1

Comparison of mean age of first concern (AOC) and age of first diagnosis (AOD) by characteristic (𝑁=6214); univariate testing by ANOVA on log-transformed AOC and AOD.

Characteristic	𝑁	Mean age at first concern (AOC), mo. (SD)*	ANOVA 𝑃  value/median	Mean age at first diagnosis (AOD), mo. (SD)*	ANOVA 𝑃  value/median
Overall	6214	19.6 (15.0)		47.6 (30.8)
Median			18 (IQR 11,24)		36.9; (IQR 27.8, 56.4)
Gender			< .001		.796
Male	5119	19.8		47.6
Female	1095	18.6		49.0
Race			.048		.367
White	5491	19.5		47.8
African-American	165	21.7		49.2
Asian/Asian-American	57	21.7		45.8
Multiracial	244	18.7		50.0
Other/unknown	257	19.6		46.4
Ethnicity			< .05		.004
Hispanic	5709	19.9		44.0
Not Hispanic	505	19.5		48.2
Current age, years*			< .001		< .001
0–5	940	14.4		29.0
6–11	3692	18.7		42.4
12–18	1582	24.7		71.9
Initial ASD Diagnosis			< .001		< .001
Autism	2535	10.5		38.3
PDD-NOS^a	1893	13.5		44.9
Asperger	891	24.4		87.8
Other ASD	895	11.9		41.7
Intellectual disability ^b (ID)			< .001		.194
Present	1229	17.8		48.3
Absent	4971	20.0		47.8
Firstborn	3242	20.6	< .001	49.1	< .001
Not firstborn	2971	18.5		46.5
History of autistic regression	1511	16.9	.854	38.2	< .001
No regression	4703	20.4		51.0
High-risk ^c			< .001		.535
Yes	650	16.0		47.4
No	5563	20.0		47.9
Multiplex family			.255		.776
Yes	872	21.0		49.4
No	5342	19.3		47.6
Era of Initial Diagnosis			.601		< .001
1994–2000	850	18.5		39.3
2001–2008	5364	19.7		49.2
Maternal education			.468		.007
≤College diploma	3098	19.5		48.9
College+	3116	19.6		46.8
County median income			.537		< .001
Lowest quartile	171	14.9		46.6
2nd quartile	486	14.9		47.2
3rd quartile	1211	16.3		51.1
4th quartile	4344	14.7		49.9
County percent white			.494		< .001
Lowest quartile	2206	19.3		46.6
2nd quartile	2453	19.4		47.2
3rd quartile	1178	20.6		51.0
4th quartile	375	19.4		49.9
Rurality ^50			.595		< .001
Large central metro	1364	19.6		45.1
Large fringe metro	2104	19.2		46.0
Medium metro	1303	19.3		48.5
Small metro	644	20.8		53.6
Micropolitan	538	20.5		51.2
Noncore (rural)	261	18.2		52.2
Binary rural			.621		< .001
Principal city ≥ 1 million	368	19.4		45.7
Principal city < 1 million	2746	19.8		50.6
US Region			.311		< .001
Northeast	1843	18.9		44.8
South	1808	19.4		50.1
Midwest	1434	20.5		49.8
West	1129	19.6		46.7

Note -: not significant. Some totals in categories do not add up to 6214 due to missing data.
^aPDD-NOS: Pervasive Developmental Disorder-Not Otherwise Specified.
^bID: Intellectual disability/mental retardation.
^cHigh risk: history of prematurity (<34 weeks gestational age) and/or seizures and/or cerebral palsy; sibling with ASD not included.