Table 1.

Participants’ demographic characteristics.

Variable	Value (n = 2,124)
Toddler’s age, mean ± SD, mo	24.2 ± 3.8
Toddler’s sex (%)
Male (n = 1,075)	50.6
Female (n = 1,049)	49.4
Attending nursery school ≥ 3 days/wk (%)	33.9
Sleeping place (%)
Bedroom	92.8
Living room	5.7
Other	1.5
Sleeping style (%)
Sleeping with caregivers	86.2
Sleeping alone	13.0
Other	0.8
Number of siblings, mean ± SD	1.3 ± 0.6
Informant (%)
Mother	78.5
Father	21.4
Grandfather	0.1
Mother’s age, mean ± SD (n = 2,105), y	34.0 ± 4.7
Father’s age, mean ± SD (n = 2,034), y	36.4 ± 5.9
Mother’s educational level (%)
Junior high school	2.0
High school	21.0
Professional training college/junior college	34.7
University graduate/completed graduate school	38.7
Other/not answered	3.6
Father’s educational level (%)
Junior high school	3.1
High school	24.6
Professional training college/junior college	15.6
University graduate/completed graduate school	53.7
Other/not answered	3.0
Working mothers (%)	40.0
Working fathers (%)	98.4
Annual income (including taxes) (%)
≤ $19,999	2.3
$20,000–$39,999	20.0
$40,000–$59,999	31.2
$60,000–$79,999	17.3
$80,000–$99,999	6.7
≥ $100,000	5.6
Do not know/no answer	16.9
Single mother (%)	2.8
Single father (%)	0

SD = standard deviation.