. 2011 Aug 1;34(8):1013–1020. doi: 10.5665/SLEEP.1152

Table 3.

Frequency of mobile phones use for sending text messages after lights out, stratified by sex and grade

		Mobile phone use for sending text messages (%)
	N	None	1-3 times/mo	Once/wk	Several times/wk	Every day	Uncertain
Male
Junior high school
7^th grade	6497	80.4	3.8	3.2	6.0	4.8	1.8
8^th grade	6769	71.5	5.0	3.9	9.4	8.6	1.5
9^th grade	6296	66.9	4.8	4.7	11.0	11.1	1.5
Senior high school
10^th grade	10154	49.4	7.0	7.4	17.6	17.4	1.1
11^th grade	9599	49.1	6.2	7.4	17.3	18.9	1.1
12^th grade	8762	51.7	5.8	6.9	16.7	17.7	1.3
Total	48077	59.3	5.7	5.9	13.8	14.0	1.3
Female
Junior high school
7^th grade	6769	64.6	7.6	5.1	11.5	10.1	1.2
8^th grade	6837	55.3	8.7	5.1	14.6	15.5	1.0
9^th grade	6575	53.0	7.2	5.3	15.3	18.0	1.2
Senior high school
10^th grade	9964	38.5	7.8	7.0	20.2	25.8	0.7
11^th grade	8662	36.8	7.6	7.5	19.4	27.8	0.8
12^th grade	7893	39.9	6.1	6.9	20.2	26.1	0.9
Total	46700	46.7	7.5	6.3	17.3	21.3	0.9