| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 0.5 | 124 |
| 2015 | 0.5 | 132 |
| 2014 | 0.4 | 139 |
| 2013 | 0.4 | 138 |
| 2012 | 0.3 | 137 |
| 2011 | 0.3 | 133 |
| 2010 | 0.3 | 136 |
| 2009 | 0.3 | 137 |
| 2008 | 0.3 | 141 |
| 2007 | 0.2 | 136 |
| 2006 | 0.2 | 139 |
| 2005 | 0.2 | 142 |
| 2004 | 0.2 | 142 |
| 2003 | 0.2 | 141 |
| 2002 | 0.2 | 136 |
| 2001 | 0.1 | 131 |
| 2000 | 0.1 | 133 |
| 1996 | 0.1 | 137 |
| 1995 | 0.1 | 134 |
| 1994 | 0.1 | 131 |
| 1993 | 0 | 133 |
| 1992 | 0 | 122 |
| 1991 | 0 | 118 |
| 1990 | 0 | 115 |
| 1989 | 0.1 | 109 |
| 1988 | 0.1 | 107 |
| 1987 | 0.1 | 105 |
| 1986 | 0.3 | 89 |