Table 3. Characteristics of the Population.

Individual level variable	Total populaition	Teenage mothers
	n	n	%
Total	21,159	440	2.1
Education
Junior-high school	1,135	202	17.8
High school or over	20,024	238	1.2
Couple's income (JPY)
< 2 million	2,027	214	10.6
≥ 2 million	19,132	226	1.2
Smoking habits
Nonsmoker	17,772	255	1.4
Smoker	3,387	185	5.5
Cohabiting with the child's father
Yes	20,429	360	1.8
No	730	80	11.0
Living in a three-generation household
Yes	4,201	227	5.4
No	16,958	213	1.3