Effect of household size on mental problems in children: results from the Norwegian Mother and Child Cohort study

Table 7 Adjusted mean scores (M) with confidence intervals (CI) of mental health related problems by household size, stratified by sex

Household size	3 years				5 years		8 years
	Eating/somatic		Hyperactivity/concentration		Difficult temperament		Anxiety
	Boys	Girls	Boys	Girls	Boys	Girls	Boys	Girls
1	.02 (-.06, .10)	.04 (-.04, .12)	.01 (-.06,. 09)	-.02 (-.10, .05)	.09 (-.14, .20)	.01 (-.10, .12)	.06 (-.07, .20)	-.05 (-.17, .07)
2	-	-	-	-	-	-	-	-
3	-.23 (-.26,-.20)	-.23 (-.26,-.30)	-.08 (-.11,-.06)	-.10 (-.12,-.07)	-.12 (-.15,-.08)	-.14 (-.18,-.11)	-.14 (-.19,-.09)	-.06 (-.11,-.01)
4	-.24 (-.28,-.20)	-.26 (-.30,-.22)	-.24 (-.28,-.20)	-.25 (-.28,-.21)	-.28 (-.33,-.24)	-.33 (-.38,-.28)	-.16 (-.22,-.10)	-.15 (-.21,-.09)
5	-.26 (-.33,-.19)	-.31 (-.38,-.23)	-.28 (-.35,-.21)	-.30 (-.37,-.23)	-.22 (-.31,-.12)	-.38 (-.48,-.28)	-.18 (-.29,-.07)	-.21 (-.33,-.08)
6+	-.25 (-.37,-.13)	-.23 (-.36,-.10)	-.22 (-.34,-.09)	-.33 (-.45,-.21)	-.38 (-.52,-.24)	-.41 (-.58,-.25)	-.15 (-.36,-.07)	-.31 (-.53,-.10)

The outcome scores are z-scaled (SD = 1) with parents only (size = 2) as reference. The results are adjusted for maternal age, maternal and paternal educational level, family income, maternal and paternal period of leave from work after birth, maternal breastfeeding status when child is 18 months, and animals in the family. Results are shown for the outcome variables for which a significant (p < .01) overall “sex X household size” interaction effect could be demonstrated; that is, comparing household size = 2 with larger households. p < 10⁻⁵ (overall test of mean differences between categories) for the effect of household size (3 and more) on all outcome variables in both genders