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Table 5 Associations between IFAS and low birth weight

From: Heckman-type selection models to obtain unbiased estimates with missing measures outcome: theoretical considerations and an application to missing birth weight data

Logit Models Heckman Models
Variable Unadjusted Adjusted Unadjusted Adjusted
Risk differential Risk differential Risk differential Risk differential
dy/dx 95% CI dy/dx 95% CI dy/dx 95% CI dy/dx 95% CI
IFA: No(+)
 Yes 0.076 −0.101; 0.253 0.061 −0.184; 0.305 0.003 −0.026; 0.031 − 0.104*** − 0.169; − 0.039
Educational attainment: No schooling(+)
 Primary school 0.064 − 0.155; 0.282    0.004 − 0.027; 0.035
 Coranic 0.016 −0.393; 0.425    −0.010 − 0.069; 0.049
 Secondary or higher − 0.239 − 0.574; 0.096    − 0.053** −0.101; − 0.005
Maternal age (years): 20–34(+)
 15–19 0.898*** 0.655; 1.141    0.126*** 0.085; 0.167
 35–49 0.569*** 0.263; 0.875    0.051** 0.004; 0.099
Socioeconomic status: Most poor(+)
 Poor −0.161 −0.488; 0.167    −0.033 −0.078; 0.013
 Middle −0.225 − 0.549; 0.100    − 0.076*** −0.126; − 0.025
 Rich 0.004 − 0.313; 0.321    − 0.051* −0.102; 0.000
 Most rich −0.178 − 0.561; 0.205    − 0.074** −0.133; − 0.016
Child sex: male
 Female 0.338*** 0.147; 0.529    0.045*** 0.019; 0.070
Previous births: 0 child (+)
 1–4 −0.473** −0.862; − 0.085    −0.065** − 0.125; − 0.005
 ≥5 −1.283*** −1.782; − 0.785    −0.148*** −0.223; − 0.072
Twin births: No(+)
 Yes 2.483*** 2.199; 2.767    0.336*** 0.288; 0.385
 Constant −1.987*** −2.115; − 1.859 −2.287*** −2.873; − 1.700     
LR test (Rho = 0) 14.59***  
 observations 4510   4510   4510   4510  
  1. *** p < 0.01. ** p < 0.05.* p < 0.1;(+) Reference category; dy/dx = Marginal effect is a change in the probability of Y = 1 with a unit change in X. Adjusted model controls for village fixed effects; CI: confidence interval