Table 1.

Sample distribution of the study population by age, sex and race/ethnicity

	2008		2011
Characteristic	n	%*	n	%*	P-value†
Age (years)
2	1 004 486	38.1	992 435	36.2
3	853 728	32.4	901 631	32.9	<0.0001
4	779 941	29.6	847 686	30.9
Sex
Boy	1 331 333	50.5	1 387 670	50.6	0.0006
Girl	1 306 822	49.5	1 354 082	49.4
Race/ethnicity
Non-Hispanic white	972 628	36.9	989 639	36.1
Non-Hispanic black	532 968	20.2	572 159	20.9
Hispanic	1 030 325	39.1	1 069 255	39.0	<0.0001
American Indian/Alaska Native	24 362	0.9	25 224	0.9
Asian/Pacific Islander	77 872	3.0	85 475	3.1

^*Percentages may not add up to 100% because of rounding.

^†P-value for χ² test compares the difference in the distribution of the study populations in 2008 and 2011.