By correlating outcomes with only the reform - induced variation in school spending (rather than all variation in spending), one removes the confounding effect of unobserved factors that might influence both school spending and student outcomes. (educationnext.org)
They obtain qualitatively similar results for this sample, suggesting that discrimination rather than unobserved differences in student experience drives the small but statistically significant result. (educationnext.org)
When we more fully account for unobserved heterogeneity between children who are breastfed and those who are not, we are forced to reconsider the notion that breastfeeding unequivocally results in improved childhood health and wellbeing. (themilkmeg.com)