The methodology we use to estimate what would happen if countries all
rebased up to 2013 is crude, but simple and involves applying an estimated
constant cumulative annual rate of growth to the years between the last reported
base year and 2013.
The longer the period between 2013 and the last base year
and the higher the assumed cumulative growth rate, the higher the uplift that
would be expected from rebasing. The resultant country uplift factor is then
applied to the 2012 World Bank GDP data for countries ranked by size in Table 3.