The $1/day figure was actually the estimate minimum survival income calculated for a number of poor countries then averaged and rounded. It's not perfect but no

The $1/day figure was actually the estimate minimum survival income calculated for a number of poor countries then averaged and rounded. It's not perfect but not arbitrary either. In fact it is now usually quoted as either $1.25 or less frequently as $1.20. Wikipedia has a pretty good article on some of the complexities involved[1]. If you use a $2/day threshold (aka "moderate poverty") instead, the declines are not quite great but still pretty damn good - down 41% - from 69% below $2 in 1981 to only 41% in 2010 (calc from data here [2]). It is not flat! And it is also not an all or nothing proposition - the entire distribution has shifted! The distribution was graphed in Economist article above. The issues with PPP are more complex but everyone involved is aware of the issues you mention[3]. While biases can occur it is not generally considered to be a problem for the global aggregates. Dig into the World Banks's ICP website for the details on PPP in poor countries[4]. [1] http://en.wikipedia.org/wiki/Measuring_poverty http://en.wikipedia.org/wiki/Measuring_poverty [2] http://www.worldbank.org/en/topic/poverty/overview http://www.worldbank.org/en/topic/poverty/overview [3] http://en.wikipedia.org/wiki/Purchasing_power_parity http://en.wikipedia.org/wiki/Purchasing_power_parity [4] http://siteresources.worldbank.org/ICPEXT/Resources/ICP_2011.html http://siteresources.worldbank.org/ICPEXT/Resources/ICP_2011...