Associations between Exposure to Tobacco Smoke and Behavioral Problems in Preschool Japanese Children

Table 1

Characteristics of 437 preschool children.

	n	Percent (%)	Total difficulty score
			Mean	Standard error
Sex
Boys	231	52.9	9.76^a	0.30	0.12
Girls	206	47.1	9.07^a	0.32
Age
≤4.5 y	133	30.4	9.62^a	0.40	0.68
>4.5 to 5.5 y	124	28.4	9.56^a	0.41
>5.5 y	180	41.2	9.21^a	0.34
Body mass index (tertiles)
Low (<14.6)	148	33.9	9.70^b	0.38	0.58
Middle (14.6–15.7)	143	32.7	9.14^b	0.38
High (>15.7)	143	32.7	9.46^b	0.38
Missing	3	0.7
Siblings
None (only child)	98	22.4	10.52^b	0.46	0.009
1st	161	36.8	9.50^b	0.36
2nd	177	40.5	8.76^b	0.34
Missing	1	0.2
Birthweight
2500 g or less	35	8.0	11.26^b	0.77	0.017
>2500 to 4000 g	399	91.3	9.25^b	0.23
More than 4000 g	3	0.7	13.08^b	2.62
Feeding until 3 months old
Breast-fed	173	39.6	8.89^b	0.34	0.006
Mix-fed	196	44.9	9.38^b	0.32
Bottle-fed	68	15.6	10.97^b	0.55
Age of mother at delivery
≤25 y	47	10.8	10.37^b	0.67	0.17
26–30 y	225	51.5	9.67^b	0.30
31–35 y	146	37.4	8.83^b	0.38
≥36 y	18	4.1	9.08^b	1.08
Missing	1	0.2
Mother’s education (years)
≤12 y	138	31.6	9.58^b	0.39	0.51
13–15 y	209	47.8	9.53^b	0.32
≥16 y	75	17.2	8.88^b	0.53
Missing	15	3.4
Mother’s depression
No	342	78.3	9.26^b	0.25	0.018
Yes	60	13.7	10.79^b	0.59
Missing	35	8.0

^aCrude mean, ^bsex- and age-adjusted mean, and ^canalysis of variance or analysis of covariance. The total difficulty score was assessed by the Strengths and Difficulties Questionnaire.