Social scientists theorize that the inverse relationship between socio-economic status and family size represents a trade-off between the quality and quantity of children. Evaluating this hypothesis empirically requires addressing the simultaneity of the quality and quantity decisions....

At least one of every five marriages is consanguineous (between couples who are second cousins or closer) in the Middle East and North Africa, and the rate is higher than 50 percent in some parts of the world. Consanguineous marriage generates serious health problems for the offspring and...