Revisiting the Relationship between WIC Participation and Breastfeeding among Low-Income Children in the U.S. after the 2009 WIC Food Package Revision

. Author manuscript; available in PMC: 2022 May 1.

Published in final edited form as: Food Policy. 2021 Apr 23;101:102089. doi: 10.1016/j.foodpol.2021.102089

	First-stage								Second-stage		IV Test Results (U: Under-identification Test W: Weak Instrument Test O: Over-identification Test)^‡
Variables	1^st Stage Regression Coeff.	SE	P-value	R²	U-Stat	P-value	W-stat	10% Cutoff Point	O-stat	P-value
SNAP Policy Index	0.010	0.006	0.101	0.161	1.89	0.17	15.20	16.38	NA	NA
Eligibility	0.011	0.006	0.063	0.161	3.38	0.07	9.71	16.38	NA	NA
Transaction	0.043	0.022	0.050	0.161	2.18	0.14	26.20	16.38	NA	NA
Stigma	0.001	0.014	0.942	0.161	0.01	0.94	0.04	16.38	NA	NA
Outreach	−0.296	0.184	0.109	0.161	2.27	0.13	6.53	16.38	NA	NA
Combination 1				0.161	4.46	0.11	17.90	19.93	0.217	0.642	O
Eligibility	0.011	0.006	0.058
Transaction	0.043	0.021	0.047
Combination 2				0.161	3.39	0.18	4.86	19.93	0.006	0.939	O
Eligibility	0.011	0.006	0.063
Stigma	0.000	0.014	0.977
Combination 3				0.161	4.69	0.10	7.35	19.93	0.526	0.468	O
Eligibility	0.011	0.006	0.082
Outreach	−0.260	0.185	0.160
Combination 4				0.161	3.59	0.17	13.45	19.93	0.012	0.912	O
Transaction	0.044	0.021	0.039
Stigma	−0.004	0.011	0.694
Combination 5				0.161	2.74	0.25	15.56	19.93	1.105	0.293	O
Transaction	0.042	0.021	0.046
Outreach	−0.258	0.157	0.102
Combination 6				0.161	2.43	0.30	3.27	19.93	<0.001	0.996	O
Stigma	0.001	0.014	0.967
Outreach	−0.296	0.181	0.104
Combination 7				0.161	5.51	0.14	12.25	9.08	0.277	0.871	O
Eligibility	0.012	0.006	0.055
Transaction	0.044	0.021	0.037
Stigma	−0.005	0.011	0.640
Combination 8				0.161	4.88	0.18	13.14	9.08	1.169	0.557	O
Eligibility	0.011	0.006	0.075
Transaction	0.042	0.021	0.043
Outreach	−0.222	0.159	0.165
Combination 9				0.161	3.87	0.28	10.64	9.08	1.161	0.560	O
Transaction	0.043	0.020	0.036
Stigma	−0.005	0.011	0.674
Outreach	−0.260	0.158	0.102

^†

Controlling state dummy, sex, race/ethnicity, education, child’s age, maternal age, maternal marital status, number of people in the household, interview language, birth year, TANF/Temporary Assistance for Needy Families enrollment rate (# of enrolled participants/# of state population), CHIP/Children’s Health Insurance Program enrollment rate (# of enrolled children/# of children 18 or under in the state), and state unemployment rate.

^‡

U means under-identification test P < 0.05. Stock–Yogo tabulations based on the Cragg–Donald statistic and used for the weak identification test; W means the F statistic of the weak identification test > 10% maximal IV relative bias or > 10% maximal IV size; O means over-identification test > 0.05.