| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 3.7 | 86 |
| 2015 | 3.8 | 92 |
| 2014 | 2.8 | 104 |
| 2013 | 2.4 | 108 |
| 2012 | 2.2 | 107 |
| 2011 | 1.9 | 112 |
| 2010 | 1.7 | 112 |
| 2009 | 1.4 | 114 |
| 2008 | 0.8 | 124 |
| 2007 | 0.8 | 121 |
| 2006 | 0.8 | 118 |
| 2005 | 0.7 | 118 |
| 2004 | 0.7 | 119 |
| 2003 | 0.7 | 113 |
| 2002 | 0.7 | 106 |
| 2001 | 0.7 | 102 |
| 2000 | 0.8 | 98 |
| 1999 | 0.9 | 97 |
| 1998 | 0.8 | 96 |
| 1997 | 1 | 92 |
| 1996 | 1.1 | 89 |
| 1995 | 1.2 | 84 |
| 1994 | 1.1 | 87 |
| 1993 | 0.4 | 103 |