The dataset by Kristian Gleditsch provides estimates of trade flows between independent states (1948-2000) and GDP per capita of independent states (1950-2011). Version 6. In order to fill in gaps in the Penn World Table's mark 5.6 and 6.2 data (see: Heston, Summers \& Aten), Gleditsch has imputed missing data by using an alternative source of data (the CIA World Fact Book), and through extrapolation beyond available time-series.