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. 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

Table 3.

First-stage Estimates of Two-stage Least Square IV Estimation of WIC Participation on Breastfeeding Practice in a WIC-eligible Population (Income ≤ 230% of the FPL) †

Variables SNAP enrollment rates (SNAP) Square of SNAP enrollment rates (SNAP2) SNAP policy index R2 U-Stat (P-value) W-stat (10% Cutoff Point) Identification test‡
Coeff. S. E P-value Coeff. S.E P-value Coeff. S.E P-value
ALL 1.563 0.382 < 0.001 −4.513 1.221 < 0.001 0.006 0.005 0.266 0.161 13.08 (< 0.01) 15.36 (9.08) UW
Boy 0.754 0.488 0.124 −2.554 1.504 0.091 0.017 0.007 0.010 0.162 4.20 (0.24) 10.40 (9.08)
Girl 2.410 0.543 < 0.001 −6.578 1.591 < 0.001 −0.006 0.007 0.411 0.164 15.71 (< 0.01) 12.49 (9.08) UW
Non-H White 1.054 0.572 0.066 −2.984 1.783 0.096 −0.009 0.010 0.353 0.170 4.27 (0.23) 2.24 (9.08)
Non-H Black 1.756 0.620 0.005 −5.784 1.781 0.001 −0.006 0.009 0.527 0.059 10.13 (0.02) 4.05 (9.08) U
Hispanic 1.322 0.769 0.087 −4.330 2.218 0.052 0.019 0.007 0.009 0.066 3.84 (0.28) 13.99 (9.08)
Other 3.019 1.072 0.005 −6.133 3.289 0.064 0.011 0.016 0.499 0.138 9.77 (0.02) 7.81 (9.08) U
†

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. IV Variables including SNAP enrollment rates (SNAP, # of SNAP participants in that year/# of state population in that year), square of SNAP enrollment rates (SNAP2), and SNAP policy index.

‡

U means the under-identification test P < 0.05. Stock–Yogo tabulations based on the Cragg–Donald statistic were 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.