| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 0.2 | 68 |
| 2015 | 0.3 | 175 |
| 2014 | 0.3 | 175 |
| 2013 | 0.1 | 176 |
| 2012 | 0.2 | 179 |
| 2011 | 0.3 | 173 |
| 2010 | 0.5 | 169 |
| 2009 | 0.2 | 172 |
| 2008 | 0.8 | 160 |
| 2007 | 0.4 | 174 |
| 2006 | 0.4 | 165 |
| 2005 | 0.2 | 164 |
| 2004 | 0 | 173 |
| 2003 | 0 | 174 |
| 2002 | 0 | 167 |
| 2001 | 0 | 163 |
| 2000 | 0 | 158 |
| 1999 | 0 | 158 |
| 1998 | 0 | 164 |
| 1997 | 0 | 170 |
| 1996 | 0 | 167 |
| 1995 | 0 | 165 |
| 1993 | 0 | 159 |
| 1989 | 0 | 128 |
| 1988 | 0 | 127 |
| 1987 | 0 | 122 |