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Table 1 Associations between IFAS and 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

Linear regressionHeckman Model
VariableUnadjusted coeffAdjusted coeffUnadjusted coeffAdjusted coeff
Coeff95% CICoeff95% CICoeff95% CICoeff95% CI
IFAS: No(+)
 Yes27.08*−3.49; 57.6622.48−13.73; 58.6938.82**6.66; 70.9753.19***12.76; 93.63
Educational attainment: No schooling(+)
 Primary19.87−13.53; 53.28  19.18−14.16; 52.53
 Coranic35.95−26.13; 98.02  34.48−27.51; 96.47
 Secondary or higher49.39**1.52; 97.27  45.12*−2.75; 92.99
Maternal age (years): 20–34(+)
 15–19−209.60***− 252.60; − 166.60  − 209.84***−252.73; − 166.95
 35–496.97−37.70; 51.63  2.54−42.12; 47.21
Socioeconomic status: Most poor(+)
 Poor33.76−16.13; 83.64  30.70−19.09; 80.50
 Middle25.64−24.09; 75.37  18.98−30.80; 68.75
 Rich−0.10−49.72; 49.52  −8.85−58.63; 40.93
 Most rich53.73*−3.79; 111.30  44.70−12.96; 102.37
Child sex: Male(+)
 Female− 124.70***−153.20; −96.19  − 123.36***− 151.74; − 94.98
Previous births: 0 child(+)
 1–454.38−18.11; 126.90  54.50−17.87; 126.87
 ≥ 5181.50***98.92; 264.10  184.51***102.08; 266.94
Twin births: No(+)
 Yes− 640.40***− 701.60; − 579.30  − 644.78***− 705.91; − 583.65
Constant2959***2937; 29802953***2855; 30512972.88***2948.28; 2997.483143.06***3026.61; 3259.52
R-squared0.001 0.143     
lambda    −47.75**−88.24; −7.25−79.24***−126.05; −32.42
observations4510 4510 7325 7325 
  1. *** p < 0.01. ** p < 0.05.* p < 0.1;(+) Reference category; Adjusted model controls village fixed effects; CI Confidence interval