Table 2.

Sleep problems, digital devices and YDQ by sex/grade

	Sex	Grade 1 n = 1310		Grade 2 n = 1252		Grade 3 n = 1278		Grade 4 n = 1199		Grade 5 n = 1162		Grade 6 n = 1282		p-trend*
		n	%	n	%	n	%	n	%	n	%	n	%
Cumulative score of the brief sleep questionnaire for Japanese children ≥24	boy	370	61.7	362	64	331	54.8	327	57.2	299	54.1	308	54.8	< 0.001
	girl	373	63.3	377	62.9	374	62.8	321	60	315	60.9	340	56.7	0.01
Having their own digital device (e.g. smartphone, tablet, PC)	boy	136	22.7	160	28.3	257	42.5	270	47.2	275	49.7	318	56.6	< 0.001
	girl	136	23.1	186	31.1	271	45.5	281	52.5	328	63.4	387	64.5	< 0.001
Checking digital devices frequently	boy	50	8.3	65	11.5	101	16.7	106	18.5	133	24.1	174	31	< 0.001
	girl	48	8.1	52	8.7	85	14.3	87	16.3	155	30	228	38	< 0.001
Using digital devices for more than 4 hours a day	boy	34	5.7	46	8.1	59	9.8	72	12.6	93	16.8	127	22.6	< 0.001
	girl	23	3.9	35	5.8	38	6.4	42	7.9	72	13.9	107	17.8	< 0.001
Five or more checks on the Young Diagnostic Questionnaire for Internet Addiction	boy	89	14.8	85	15	116	19.2	137	24	139	25.1	165	29.4	< 0.001
	girl	47	8	61	10.2	69	11.6	67	12.5	86	16.6	117	19.5	< 0.001
Do you think your child is preoccupied with the Internet?	boy	324	54	309	54.6	342	56.6	333	58.2	330	59.7	363	64.6	< 0.001
	girl	237	40.2	262	43.7	281	47.1	246	46	281	54.4	340	56.7	< 0.001
Do you think your child needs to use the Internet with increasing amounts of time in order to achieve satisfaction?	boy	245	40.8	233	41.2	288	47.7	286	50	294	53.2	342	60.9	< 0.001
	girl	192	32.6	220	36.7	224	37.6	239	44.7	276	53.4	339	56.5	< 0.001
Do you think your child repeatedly made unsuccessful efforts to control, cut back, or stop Internet use?	boy	180	30	168	29.7	191	31.6	213	37.2	217	39.2	240	42.7	< 0.001
	girl	106	18	128	21.4	141	23.7	132	24.7	153	29.6	198	33	< 0.001
Do you think your child feels restless, moody, depressed, or irritable when attempting to cut down or stop Internet use?	boy	170	28.3	164	29	191	31.6	179	31.3	199	36	224	39.9	< 0.001
	girl	89	15.1	107	17.9	118	19.8	98	18.3	115	22.2	142	23.7	< 0.001
Do you think your child stays on-line longer than originally intended?	boy	198	33	209	36.9	214	35.4	260	45.5	270	48.8	303	53.9	< 0.001
	girl	133	22.6	176	29.4	172	28.9	181	33.8	198	38.3	261	43.5	0.001
Do you think your child jeopardized or risked the loss of a significant relationship, educational, or extracurricular activities because of the Internet?	boy	10	1.7	12	2.1	22	3.6	25	4.4	20	3.6	31	5.5	< 0.001
	girl	2	0.3	7	1.2	11	1.8	13	2.4	14	2.7	32	5.3	< 0.001
Do you think your child lied to family members, a therapist, or others to conceal the extent of involvement with the Internet?	boy	46	7.7	50	8.8	61	10.1	75	13.1	82	14.8	113	20.1	< 0.001
	girl	16	2.7	37	6.2	46	7.7	50	9.3	48	9.3	61	10.2	< 0.001
Do you think your child uses the Internet as a way of escaping from problems or relieving a dysphoric mood?	boy	22	3.7	20	3.5	42	7	43	7.5	48	8.7	57	10.1	< 0.001
	girl	16	2.7	11	1.8	28	4.7	25	4.7	43	8.3	43	7.2	< 0.001

*Cochrane Armitage trend test was done to examine grade trends