Table 3.

Participant characteristics and quality of sleep

	Subjective sleep quality					Sleep latency					Sleep duration					Habitual sleep efficiency
	No-risk group		Risk group			No-risk group		Risk group			No-risk group		Risk group			No-risk group		Risk group
	n	%	n	%	p	n	%	n	%	p	n	%	n	%	p	n	%	n	%	p
Sex
Male	89	30.7	201	69.3	0.913	166	59.1	115	40.9	0.195	269	92.8	21	7.2	0.238	277	97.9	6	2.1	0.708
Female	93	31.1	206	68.9		159	53.7	137	46.3		271	90.0	30	10.0		290	98.3	5	1.7
Family composition
Single-parent household	7	17.9	32	82.1	0.070	18	42.9	24	57.1	0.068	36	90.0	4	10.0	0.749	35	94.6	2	5.4	0.107
Two-parent household	175	31.8	375	68.2		307	57.4	228	42.6		504	91.5	47	8.5		532	98.3	9	1.7
Annual household income (¥)
< 3,000,000	5	11.6	38	88.4	0.029	18	41.9	25	58.1	0.281	40	87.0	6	13.0	0.642	42	97.7	1	2.3	0.150
3,000,000–6,000,000	81	33.8	159	66.3		134	57.3	100	42.7		222	92.1	19	7.9		229	98.3	4	1.7
6,000,000–9,000,000	50	30.3	115	69.7		93	57.4	69	42.6		151	92.1	13	7.9		156	96.3	6	3.7
≥ 9,000,000	45	34.4	86	65.6		73	57.0	55	43.0		117	90.0	13	10.0		130	100.0	0	0.0
Mother’s educational background
Middle school or high school	27	25.5	79	74.5	0.331	48	46.6	55	53.4	0.088	98	93.3	7	6.7	0.322	92	94.8	5	5.2	0.039
Junior college or vocational school	73	31.3	160	68.7		134	59.0	93	41.0		210	89.4	25	10.6		228	98.7	3	1.3
University or graduate school	82	33.5	163	66.5		140	57.9	102	42.1		228	92.7	18	7.3		242	98.8	3	1.2
Father’s educational background
Middle school or high school	43	32.1	91	67.9	0.812	73	57.0	55	43.0	0.970	120	90.2	13	9.8	0.763	123	97.6	3	2.4	0.447
Junior college or vocational school	21	28.4	53	71.6		42	58.3	30	41.7		69	92.0	6	8.0		72	100.0	0	0.0
University or graduate school	116	32.1	245	67.9		202	56.7	154	43.3		334	92.3	28	7.7		352	98.1	7	1.9

χ² analysis. Bold numbers indicate statistically significant differences