The data is obtained from the Penn World Tables:

Feenstra, Robert C.; Inklar, Robert, and Timmer, Marcel P.  The next generation ofthe penn world table.American Economic Review, 105(10):3150–3182, 2015.  doi:DOI:10.1257/aer.20130954.

The Mathematica notebook Fill_PWTdata.nb imports the raw data and carries out the extrapolation and calculations.
