Table 2.

Sleep variables in early childhood and socio-emotional functioning at 24 months

Sleep variables in early childhood
	Mean (SD)	Median	Minimum	Maximum
BISQ total sleep duration, hours
3 months	14.3 (1.8)	14.5	6.0	20.0
8 months	13.3 (1.2)	13.5	9.0	20.0
18 months	12.3 (0.9)	12.2	8.0	16.0
24 months	11.9 (0.9)	12.0	8.3	15.0
BISQ proportion daytime sleep
3 months	36.2 (8.2)	36.4	10.0	77.8
8 months	25.5 (6.5)	25.0	10.0	53.8
18 months	16.7 (4.9)	16.0	6.0	39.3
24 months	15.7 (5.0)	15.9	0.0	40.0
BISQ bedtime, hh:mm
3 months	21:48 (1:11)	21:32	18:00	02:10
8 months	20:52 (0:54)	21:00	18:20	01:30
18 months	20:42 (0:42)	20:30	18:30	23:40
24 months	20:55 (0:40)	21:00	18:45	23:30
ISQ sleep-onset latency
3 months	1.9 (1.8)	1.0	0.0	6.0
8 months	1.1 (1.2)	1.0	0.0	6.0
18 months	1.0 (1.1)	1.0	0.0	6.0
24 months	1.4 (1.5)	1.0	0.0	6.0
ISQ number of night wakings
3 months	1.6 (1.3)	2.0	0.0	5.0
8 months	2.0 (1.4)	2.0	0.0	5.0
18 months	1.0 (1.2)	1.0	0.0	5.0
24 months	1.0 (1.0)	1.0	0.0	5.0

Socio-emotional functioning at 24 months
Symptom scores	Mean (SD)	Median	Minimum	Maximum
BITSEA externalising	3.1 (2.2)	3.0	0.0	11.0
BITSEA internalising	1.6 (1.5)	1.0	0.0	9.0
BITSEA dysregulation	3.1 (2.4)	3.0	0.0	12.0

BISQ variables are all continuous variables, while ISQ sleep-onset latency and ISQ number of night wakings are categorical variables: in ISQ sleep-onset latency, 0=<10 min; 1=10–19 min; 2=20–29 min; 3=30–39 min; 4=40–49 min; 5=50–59 min; and 6=≥60 min; and in ISQ number of night wakings, 0=0 times/night; 1=once/night; 2=twice/night; 3=three times/night; 4=four times/night; and 5=five times/night.

BISQ=Brief Infant Sleep Questionnaire; BITSEA, Brief Infant-Toddler Social and Emotional Assessment; ISQ, Infant Sleep Questionnaire.