Table 1 Descriptive characteristics of analytic sample (N = 6113)^a.

Continuous variables	Mean	SD	Range
Maternal age	28.27	4.68	15–44.1
SDQ hyperactivity score^b at 10 (114 months)	3.14	2.23	0–10
SDQ hyperactivity score^b at 13 (156 months)	3.23	2.21	0–10
MFQ score^c at 10 (127 months)	4.32	3.60	0–22.07
MFQ score^c at 13 (154 months)	4.24	3.94	0–24
SCDC^d scored at 10 (120 months)	2.91	3.79	0–24
SCDC^d scored at 13 (156 months)	3.29	3.97	0–24
BMI z-score^e at 10 (127 months)	0.34	1.16	−3.65 to 4.26
BMI z-score^e at 13 (154 months)	0.41	1.20	−3.83 to 4.55
GCSE capped points score	332.34	87.36	0–540
	Median	IQR	Range
Percent of sessions absent, year 11 (age 15–16)	5.53	7.28	0–98.59
Percent of sessions absent, year 10 (age 14–15)	4.83	6.71	0–90.39
Percent of sessions absent, key stage 4 (age 14–16)	5.42	6.34	0–79.29
Categorical variables	Category		%
Gender	Male		49.99
Gender	Female		50.01
Maternal educational qualifications	CSE or less		16.77
	vocational		9.49
	O level		35.94
	A level		24.33
	Degree		13.47
Maternal parity at child’s birth	0		44.9
	1		36.15
	2		14.00
	3+		4.94
Migraines at 10	No		95.03
Migraines at 10	Yes		4.97
Asthma at 10 (128 months)	No		87.77
Asthma at 10 (128 months)	Yes		12.23
Asthma at 13 (157 months)	No		87.99
Asthma at 13 (157 months)	Yes		12.01
School type^f at key stage 4 (age 14–16)	Mainstream state		93.13
	Independent		5.45
	Other		1.42

^aAnalysis was restricted to unrelated ALSPAC participants with genetic data and linked GCSE records. Missing data in covariates, exposures and school absence was imputed using multiple imputation by chained equations.
^bSDQ = Strengths and Difficulties Questionnaire, for ADHD symptoms.
^cMFQ = Mood and Feelings Questionnaire, for depressive symptoms.
^dSCDC = Social Communication Disorder Checklist, for autistic social traits.
^eUsing 1990 UK Growth Reference. Values represent standard deviation difference from age-specific and gender-specific reference mean.
^fMainstream state schools: community, voluntary controlled or aided, foundation, city technology college, academy. Other schools: community special, pupil referral unit, further education college.

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