Martin Medina (March 2005). "Waste Picker Cooperatives in Developing Countries". WIEGO/ Cornell/ SEWA Conference on Membership-Based Organizations of the Poor. Mexico City: El Colegio de la Frontera Norte.2005 .
This figure is obtained by taking 2% of the population of cities with more than 1 million inhabitants in low-income countries, i.e. 2% of 12% of 686.5 million inhabitants, according to World Bank data. If we also take the population of cities with more than 1 million inhabitants in countries with lower middle income, we add 2% of 18% of 1,320 million people. http://devdata.worldbank.org/wdipdfs/table3_10.pdf