Compare methods

	Poverty Gap Index	Datt-Ravallion Decomposition
Field	Economics	Economics
Family	Process / pipeline	Process / pipeline
Year of origin	1984	1992
Originator	James Foster, Joel Greer & Erik Thorbecke (FGT alpha = 1)	Gaurav Datt & Martin Ravallion
Type	Money-metric poverty depth measure	Poverty-change decomposition
Seminal source	Foster, J., Greer, J., & Thorbecke, E. (1984). A class of decomposable poverty measures. Econometrica, 52(3), 761–766.	Datt, G., & Ravallion, M. (1992). Growth and redistribution components of changes in poverty measures: a decomposition with applications to Brazil and India in the 1980s. Journal of Development Economics, 38(2), 275–295.
Aliases	Poverty Gap Ratio, Income Gap Measure, Mean Normalized Shortfall, Depth of Poverty	Growth-Redistribution Decomposition, Datt-Ravallion Method, Growth and Redistribution Components, Poverty Change Decomposition
Related	3	3
Summary	The poverty gap index is the member of the Foster-Greer-Thorbecke family at alpha = 1 and the standard money-metric measure of the depth of poverty. Where the headcount ratio merely counts who is poor, the poverty gap averages how far the poor fall below the poverty line, expressed as a fraction of that line and spread over the whole population. It can be read as the per-capita resource shortfall — the share of the poverty line, per person, that perfect targeting would need to transfer to eliminate poverty — making it the natural complement to the headcount when judging the cost and intensity of poverty.	The Datt-Ravallion decomposition, introduced by Gaurav Datt and Martin Ravallion in 1992, separates the observed change in a poverty measure between two dates into a growth component — the change attributable to a shift in mean income holding the relative distribution fixed — and a redistribution component — the change attributable to a shift in the Lorenz curve holding mean income fixed. A residual captures the interaction between the two. It became the standard way to ask whether falling poverty was driven by rising average incomes or by changes in inequality, and underlies the empirical literature on pro-poor growth.