| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 1.5 | 108 |
| 2015 | 1.5 | 114 |
| 2014 | 1.8 | 117 |
| 2013 | 1.7 | 117 |
| 2012 | 1.5 | 117 |
| 2011 | 1.4 | 115 |
| 2010 | 1.2 | 116 |
| 2009 | 1.3 | 115 |
| 2008 | 1.2 | 119 |
| 2007 | 1.1 | 117 |
| 2006 | 0.7 | 121 |
| 2005 | 0.7 | 117 |
| 2004 | 0.7 | 120 |
| 2003 | 0.5 | 122 |
| 2002 | 0.4 | 118 |
| 2001 | 0.4 | 116 |
| 2000 | 0.4 | 118 |
| 1999 | 0.4 | 116 |
| 1998 | 0.4 | 115 |
| 1997 | 0.4 | 120 |
| 1996 | 0.4 | 118 |
| 1995 | 0.4 | 109 |
| 1994 | 0.3 | 111 |
| 1993 | 0.4 | 106 |
| 1992 | 0.5 | 96 |
| 1991 | 0.7 | 90 |
| 1990 | 0.8 | 89 |
| 1989 | 0.7 | 86 |
| 1988 | 0.6 | 86 |
| 1987 | 0.5 | 83 |
| 1986 | 0.5 | 77 |