Table 1.

Summary statistics for US children born 1990–2011, by survey year

	Mean/proportion (standard deviation)
Survey year:	2003	2007	2011
Food allergy	0.042	0.052	–
	(0.201)	(0.222)	(–)
Asthma	0.110	0.132	0.142
	(0.313)	(0.339)	(0.349)
Eczema	0.111	0.125	–
	(0.315)	(0.331)	(–)
Male	0.511	0.519	0.515
	(0.500)	(0.500)	(0.500)
Female	0.489	0.481	0.485
	(0.500)	(0.500)	(0.500)
Age	6.520	9.168	8.866
	(4.141)	(5.340)	(5.242)
Black	0.108	0.109	0.102
	(0.310)	(0.312)	(0.302)
White	0.794	0.784	0.739
	(0.405)	(0.412)	(0.439)
‘Other race’	0.098	0.107	0.159
	(0.298)	(0.309)	(0.366)
Hispanic	0.091	0.087	0.132
	(0.287)	(0.282)	(0.338)
Birth year range	1990–2003	1990–2007	1994–2011
Observations	70,789	85,971	92,825

Notes: Each survey wave includes children aged 0–17, but because method of delivery data were not collected before 1990, the 2003 survey year includes a narrower range of birth years. We do not include observations with missing race, Hispanic origin, or C-section data in the summary statistics. Summary statistics report the maximum number of observations across all variables in each survey year, thus hiding minor differences in the number of missing observations by health outcome. For this reason, the summed number of observations across survey years does not perfectly correspond to the total observations in Table 2, which reports observations for each health outcome across multiple survey waves.

Source: NSCH waves 2003, 2007, and 2011.