The US dollar and the Japanese yen have been the currencies most heavily used in carry trade transactions since the 1990s. There is some substantial mathematical evidence in macroeconomics that larger economies have more immunity to the disruptive aspects of the carry trade mainly due to the sheer quantity of their existing currency compared to the limited amount used for FOREX carry trades, [ citation needed ] but the collapse of the carry trade in 2008 is often blamed within Japan for a rapid appreciation of the yen . As a currency appreciates, there is pressure to cover any debts in that currency by converting foreign assets into that currency. This cycle can have an accelerating effect on currency valuation changes. When a large swing occurs, this can cause a carry reversal. The timing of the carry reversal in 2008 contributed substantially to the credit crunch which caused the 2008 global financial crisis , though relative size of impact of the carry trade with other factors is debatable. A similar rapid appreciation of the US dollar occurred at the same time, and the carry trade is rarely discussed as a factor for this appreciation.