)٠٣( Robert J. Barro and Xavier Sala i Martin &quot; Convergence across States and Regions &quot; Brookings Papers on Economic Activity (1) 1991, &quot; Convergence &quot; Journal of Political Economy (April 1992) and Steve Dowrick and Duc-Tho Nguyen &quot; OECD Comparative Economic Growth 1950-85: Catch-up and Convergence &quot; American Economic Review (December 1989).
30/ Robert J. Barro and Xavier Sala i Martin, &quot; Convergence across States and regions &quot; , Brookings Papers on Economic Activity (1), 1991; &quot; Convergence &quot; , Journal of Political Economy (April 1992); и Steve Dowrick and Duc-Tho Nguyen, &quot; OECD comparative economic growth 1950-85: catch-up and convergence &quot; , American Economic Review (December 1989).