Source: Martin Ravallion, National Bureau of Economic Research (NBER), NBER Working Paper No. w20791, December 2014
From the abstract:
The traditional approach to poverty measurement puts no explicit weight on success at increasing the typical level of living of the poorest – raising the consumption floor. To address this deficiency, the paper defines and measures the expected value of the floor, allowing for transient effects and measurement errors in survey data. On using all suitable and available surveys for the developing world over 1981-2011, the expected value of the floor is about half the $1.25 a day poverty line. There has been only modest progress in raising the floor, despite much progress in reducing the number living near the floor.