28Loeb, Mitchell. "International Measurement of Disability."International Census/Survey Data and the Short Set of Disability Questions Developed by the Washington Group on Disability Statistics (2016).
56Van der Berg, Servaas, Cobus Burger, Ronelle Burger, Mia Vos, Gideon Rand, Martin Gustafsson, Eldridge Moses, Debra Shepherd, Nicholas Spaull, and Stephen Taylor. "Low quality education as a poverty trap." (2011).