To a first approximation, one could assume that the rate of bias is constant, and does not account for the estimated decline in productivity growth and that we should not dismiss the slowdown as an artifact of measurement difficulties.2 That is the conclusion most researchers reach, but the data issue is not settled.
Chart 2  Share of the World's Middle-Income Class 2009  2030 (Projection)  28%  34%  66%  72%  Asia  Rest of the World  Note: The share of the number of people with daily per capita income of between 10 and 100 U.S. dollars in terms of purchasing power parity.