We say “tendencies” because other things than those mentioned matter too, and may at times be substantial drivers of the patterns we see in the data. For example, a major source of exchange rate fluctuations in New Zealand is the outlook for the world prices of our commodity exports and the terms of trade.
The United States’ average contribution to global growth, on the other hand,  BIS Review 103/2006  1  has decreased from 23,3 per cent in the 1980s to 20,2 per cent in the 1990s and further to 16,3 per cent since 2000.