Table 1.

Characteristics of multiply imputed sample by the timing of diagnosis for autism spectrum disorder (ASD, N = 11,320).

	No ASD (0) n = 11,307	ASD (n = 396)					p a	Significant group differenceb
		Age 5 (1) n = 61	Age 7 (2) n = 65	Age 11 (3) n = 138	Age 14 (4) n = 132	Total n = 396
	%	%	%	%	%	%
Sex of the child							<0.001	0 vs 1,2,3,4 1 vs 3,4
Male	50.2	91.2	77.2	79.5	75.0	79.3
Female	49.8	8.8	22.8	20.5	25.0	20.7
Cognitive ability							0.12	–
Within typical range	96.0	89.0	88.5	91.8	91.7	90.8
Below 1 SD	4.0	11.0	11.5	8.2	8.3	9.2
Parental highest educationc							0.44	–
A-level or above	43.1	32.7	45.5	44.2	35.7	39.4
Below A-level	56.9	67.3	54.5	55.8	64.3	60.6
Low household incomed							0.002	0 vs 2,4
No	64.4	58.0	48.9	55.3	46.2	51.4
Yes	35.6	42.0	51.1	44.7	53.8	48.6
Parental depression							0.43	–
No	84.1	90.9	84.9	82.0	78.5	82.6
Yes	15.9	9.1	15.1	18.0	21.5	17.4
Parent-rated emotional symptoms at age 5, mean (SE)	1.4 (0.0)	2.6 (0.3)	2.9 (0.4)	1.9 (0.2)	2.4 (0.2)	2.4 (0.1)	<0.001	0 vs 1,2,3,4 1,2 vs 3
Level of ASD-related behaviours, mean (SE)e	–0.2 (0.1)	7.3 (0.9)	6.9 (1.0)	5.4 (0.6)	4.2 (0.6)	5.5 (0.4)	<0.001	0 vs 1,2,3,4 1,2 vs 4

ASD: autism spectrum disorder; SD: standard deviation; SE: standard error..

Weighted percentages are shown. Variables are measured at age 5 interview of the study unless otherwise mentioned.

^ap-value for group difference (i.e. No ASD, Age 5, 7, 11 and 14 groups) obtained using Stata command ‘contrast’ which performs analysis of variance style test of main effects and post hoc tests.

^bSignificant difference was defined as a difference at 5% levels.

^cA-levels are final examinations usually taken at age 18 before university entrance.

^dBelow 60% median of UK national household income.

^eA score indicating the level of ASD-related behaviours measured from teacher and parent reports when the child was around age 5 to 7.