Between 1970 and 2006, the global poverty rate has been cut by nearly three quarters. The percentage of the world population living on less than $1 a day (in PPP-adjusted 2000 dollars) went from 26.8% in 1970 to 5.4% in 2006 (Figure 1).

Although world population has increased by about 80% over this time (World Bank 2009), the number of people below the $1 a day poverty line has shrunk by nearly 64%, from 967 million in 1970 to 350 million in 2006. In the past 36 years, there has never been a moment with more than 1 billion people in poverty, and barring a catastrophe, there will never be such a moment in the future history of the world.

And later:

We can compute not only the world poverty rates and the poverty rates of any country or region, but also other statistics related to the distribution of income. For instance, we can compute the world gini coefficient, a measure of world inequality, for every year between 1970 and 2006. We show that world inequality measured by the gini fell from 67.6 to 61.2 (Figure 3), and similar declines in inequality can be shown for other inequality statistics, such as the mean logarithmic deviation, the Theil Index, and the Atkinson family of inequality indices.

Finally, for many theoretical concepts of welfare (e.g. Atkinson’s expected utility for the society, or Sen’s real national income) it is possible to find an inequality index described above such that the welfare concept can be represented as GDP multiplied by one minus the inequality index. Since we can compute these inequality indices, we can show that because world inequality fell, welfare measured for the world as a whole grew even faster than world GDP did, and more than doubled over the period 1970-2006.