Assessment of selection bias in a health survey of children and families – the IDEFICS Sweden-study

BMC Public Health

Table 1 Comparison of the baseline characteristics of the IDEFICS and reference populations

		IDEFICS population	Reference population	p-value
		N=1 825	N=1 825	p-value
Gender	Male	937 (51.3%)	937 (51.3%)
	Female	888 (48.7%)	888 (48.7%)	1.000
Age (years)		6.16 (2.04)	6.16 (2.04)	0.985
Place of residence	Partille	914 (50.1%)	914 (50.1%)
	Alingsås	333 (18.2%)	338 (18.5%)
	Mölndal	578 (31.7%)	573 (31.4%)
Children’s characteristics at birth	Birth weight (kg)^a	3.53 (0.57)	3.53 (0.57)	0.693
Children’s characteristics at birth	Birth weight (kg)^a	n = 1 742	n = 1 598	0.693
	Birth length (cm)^a	50.5 (2.4)	50.5 (2.4)	0.612
	Birth length (cm)^a	n = 1 726	n = 1 586	0.612
	Ponderal index (kg/m³)^a	27.3 (2.6)	27.3 (2.7)	0.757
	Ponderal index (kg/m³)^a	n = 1 726	n = 1 586	0.757
	Large for gestational age (LGA)^b	50 (3.8%)	40 (2.7%)	0.113
	Large for gestational age (LGA)^b	n = 1 316	n = 1 481	0.113
	Small for gestational age (SGA)^b	27 (2.1%)	33 (2.2%)	0.884
	Small for gestational age (SGA)^b	n = 1 286	n = 1 500	0.884

The matching between groups and children's characteristics at birth is shown. Data are presented as number and percent (%) or the mean with standard deviation (SD).
^a Children’s birth weights and lengths are derived from; register data, and the anthropometric data from Child Health Centres and School Health Services.
^b LGA, SGA variables were derived from register data.

ISSN: 1471-2458