Table 2. Prevalence of smoking among Japanese medical students.

	n	95% CI		n	95% CI
Total	1619 (13.7%)	12.0–15.4	Parent smoker (n = 1613)
			No	1149 (12.6%)	10.7–14.5
Sex (n = 1619)			Yes	464 (16.6%)	13.2–20.0
Male	1074 (18.1%)	15.8–20.4
Female	545 (5.1%)	3.3–6.9	Sibling smoker (=1617)
			No, or no sibling	1272 (11.2%)	9.5–12.9
Age (years) (n = 1619)			Yes	345 (22.9%)	18.5–27.3
21–24	1364 (12.0%)	10.3–13.7
25–29	200 (24.5%)	18.5–30.5	Drinking alcohol (n = 1617)
30–	55 (16.4%)	6.6–26.2	No	1291 (10.8%)	9.1–12.5
			Yes	326 (24.8%)	20.1–29.5
Type of university (n = 1619)
National/public	1161 (10.9%)	9.1–12.7	Drinking coffee (n = 1619)
Private	458 (20.7%)	17.0–22.4	No	761 (9.6%)	7.5–11.7
			Yes	858 (17.4%)	14.9–19.9
Smoking restriction (n = 1619)
Total smoking ban	517 (13.3%)	10.4–16.2	Participate in school club activities (n = 1617)
Designated smoking area	1102 (13.9%)	11.9–15.9	No	347 (16.7%)	12.8–20.6
			Yes	1270 (12.9%)	11.1–14.7
Cigarette vending machines (n = 1538)
No	1353 (14.5%)	12.6–16.4	Exercise (n = 1619)
Yes	185 (6.5%)	2.7–9.7	No	978 (13.8%)	11.6–16.0
			Yes	641 (13.6%)	10.9–16.3
Sale of cigarettes in campus store (n = 1302)
No	1031 (14.0%)	11.9–16.1	Insomnia (n = 1619)
Yes	271 (13.7%)	9.6–17.8	No	1332 (12.1%)	10.3–13.9
			Yes	287 (21.3%)	16.6–26.0
Passive smoking exposure (days/wk) (n = 1540)
0–3	1208 (7.4%)	5.9–8.9	Sleep duration (hours; n = 1616)
4–7	332 (33.4%)	28.3–38.5	6>	350 (17.1%)	13.2–21.0
			6≦	1266 (12.8%)	11.0–14.6
Did you learn about smoking at school? (n = 1609)
Yes	1298 (13.4%)	11.5–15.3	ESS (Daytime sleepiness) (n = 1562)
No	311 (15.4%)	11.4–19.4	11>	1362 (13.7%)	11.9–15.5
			11≦	200 (12.0%)	7.5–16.5
			GHQ (n = 1600)
			4>	949 (13.9%)	11.7–16.1
			4≦	651 (13.4%)	10.8–16.0

Data were collected from December 2006 through March 2007.

For each item, the subjects who did not answer the related questions were excluded.

ESS: Epworth Sleepiness Scale.

GHQ: General Health Questionnaire.