The well-known data set of real GDP for 130 countries over 35 years, compiled by Summers and Heston (1988), together with population figures, have been used by many economists in studying income convergence patterns between rich and poor countries. The works include those of: Baumol (1986), followed by Dowrick and Gemmell (1988), Barro (1991), Mankiw, Romer and Weil (1992), Sprout and Weaver (1992), and Theil and Seale (1994). Taking all the rich versus all poor countries together, the statistical material shows that there is a slight catching up tendency. Further disaggregration has highlighted a convergence of income levels within the richer countries but divergence within the poorer countries with some of the latter even falling behind the rest and becoming relatively poorer. These trends can be readily seen from table 8.1.