1. Firebaugh, Glenn. (2004). Does industrialization no longer benefit poor countries? A comment on Arrighi, Silver, and Brewer. Studies in Comparative International Development, 39(1), 99-105. Retrieved from http://sites.jmu.edu/benbrewer/files/2011/01/SCID-Firebaugh.pdf
2. Human Development Data (1990-2015). Human Development Reports. United Nations Development Programme. Retrieved from http://hdr.undp.org/en/data
3. Milanovic, Branko, Lindert, Peter, & Williamson, Jeffrey. (2007, October). Measuring Ancient Inequality. National Bureau of Economic Research. MPRA Paper No. 5388. Retrieved from https://mpra.ub.uni-muenchen.de/5388/1/MPRA_paper_5388.pdf
4. Milanovic, Branko, Lindert, Peter H., & Williamson, Jeffrey G. (2010). Pre-Industrial Inequality. The Economic Journal, 121 (March), 255-272. doi:10.1111/j.1468-0297.2010.02403.x. Retrieved from https://gc.cuny.edu/CUNY_GC/media/CUNY-Graduate-Center/PDF/Centers/LIS/Milanovic/papers/2011/MLW_final.pdf
5. Ortiz, Isabel, & Cummins, Matthew. (2011). Global Inequality: Beyond the Bottom Billion. A Rapid Review of Income Distribution in 141 Countries. United Nations Children’s Fund (UNICEF). Retrieved from https://www.unicef.org/socialpolicy/files/Global_Inequality.pdf