Is global inequality (inequality among world citizens) stable, decreasing or increasing? How high it is? Is it mostly due to inequalities within nations or between nations? Is there a global middle class? How did historically global inequality evolve?
For all of this, see the working papers:
Household survey data (1988-2005) used in these papers, and in books Worlds Apart: Measuring International and Global Inequality (Princeton University Press, 2005) and The haves and the Have-nots: a Brief and Idiosyncratic History of global inequality (Basic books, 2010) can be downloaded here. The data are in Stata10 and for five benchmark years: 1988, 1993, 1998, 2002 and 2005.