Evidence in the medical and epidemiological literature has documented that germs in feces can stunt children’s growth. This is in part due to diarrhea, and possibly in part due to enteropathy (Humphrey, 2009): chronic changes in the lining of the intestines (Korpe and Petri, 2012) that make it harder for the body to use nutrients. Well-identified econometric papers have also shown a causal link from sanitation to child height. For example, in a paper coauthored with Jeffrey Hammer about an experiment done in partnership with the World Bank Water and Sanitation Program and the government of Maharashtra, we find that a program that promoted rural sanitation also caused children to grow taller (Hammer and Spears, 2012). Therefore, the new working paper (Spears, 2013) asks the quantitative, accounting question: how big is the effect of sanitation on child height? Big enough to account for important differences?