FTP, identify this graph used to calculate the Gini coefficient which is employed to plot the income inequality in a population.
Because one of the elements plotted on this curve cannot be negative, the curve must be increasing and convex to the y axis.  The creator of this curve was inspired by his teacher Richard Ely at the University of Wisconsin.  Ely's book, Studies in the Evolution of Industrial Society, discussed "concentration and diffusion" as a central problem in economic analysis.  An early alternative to this curve was proposed by George Holmes, but the originator of this curve objected, noting that the difference between two medians depends on the total level of income.  The curve plots along the x axis cumulative percents of the population from poorest to richest, as compared to the cumulative percent of income each group holds.  FTP, identify this graph used to calculate the Gini coefficient which is employed to plot the income inequality in a population.
Because one of the elements plotted on this curve cannot be negative, the curve must be increasing and convex to the y axis.  
Lorenz curve