Table 1. Weighted descriptive statistics for study variables for women aged 18–49 who participated in the NHANES physical examination during 1999–2006, before and after multiple imputation of missing values.

		Pre-imputed weighted descriptive statistics			Imputed weighted descriptive statisticsa
		Mean or %	SE	n	Mean or %	SE	95% CI
Iron Status	Hemoglobin (g/dL)	13.50	0.37	6225	13.50	0.036	13.43, 13.57
	Ferritin (ng/mL)	57.84	1.03	6162	57.72	1.05	55.67, 59.78
	% Transferrin saturation	3.57	0.037	2824	3.70	0.042	3.61, 3.78
	Transferrin receptor (mg/L)b	22.60	0.19	6153	22.58	1.18	22.22, 22.94
Reproductive Status	% Pregnant	6.43	0.32	6463	6.52	0.32	5.89, 7.16
	Parity	1.54	0.028	5616	1.53	0.027	1.47, 1.58
	% Currently breastfeeding	2.01	0.34	5107	1.90	0.33	1.26, 2.53
	% Currently using hormonal contraceptive	16.02	0.84	5608	15.86	0.78	14.33, 17.39
	% Ever used hormonal contraceptive	77.46	0.86	5942	77.00	0.87	75.28, 78.70
	% Had regular periods in past year	72.40	0.83	5947	72.58	0.84	70.92, 74.23
	Age at menarche (years)	12.60	0.028	5854	12.60	0.027	12.55, 12.65
Covariates	% Hispanic	15.47	0.13	6603	15.47	0.13	–c
	% Non-Hispanic black	13.48	0.11	6603	13.48	0.11	–c
	% Non-Hispanic white	65.45	0.10	6603	65.45	0.10	–c
	% Other	5.60	0.045	6603	5.60	0.045	–c
	BMI (kg/m2)	27.86	0.16	6468	27.87	0.16	27.56, 28.19
	CRP (g/L)	0.47	0.014	6173	0.47	0.014	0.44, 0.50
	Age (years)	33.99	0.17	6603	33.99	0.17	–c
	Dietary iron intake (mg)	13.73	0.14	6252	13.73	0.14	13.46, 14.00

^aAll n  =  6603 (except transferrin receptor).

^bThe n for the imputed mean for transferrin receptor is 3295; based on 2003–2006 survey years only.

^cAll variables were available in original data set, so no 95% CI were generated by PROC MIANALYZE.