| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 4.6 | 78 |
| 2015 | 5.4 | 79 |
| 2014 | 5.4 | 80 |
| 2013 | 3.9 | 90 |
| 2012 | 4.1 | 85 |
| 2011 | 4.4 | 83 |
| 2010 | 4 | 84 |
| 2009 | 3 | 97 |
| 2008 | 2.7 | 99 |
| 2007 | 2.3 | 98 |
| 2006 | 2 | 98 |
| 2005 | 1.9 | 95 |
| 2004 | 1.7 | 97 |
| 2003 | 1.3 | 99 |
| 2002 | 0.9 | 101 |
| 2001 | 1 | 95 |
| 2000 | 0.9 | 96 |
| 1999 | 1.1 | 96 |
| 1998 | 0.8 | 98 |
| 1997 | 0.8 | 99 |
| 1996 | 0.7 | 102 |
| 1995 | 0.7 | 95 |
| 1994 | 0.6 | 98 |
| 1993 | 0.7 | 95 |
| 1992 | 1.2 | 80 |
| 1991 | 1.4 | 76 |