| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 0.8 | 117 |
| 2015 | 0.7 | 126 |
| 2014 | 0.8 | 128 |
| 2013 | 0.7 | 130 |
| 2012 | 0.6 | 131 |
| 2011 | 0.6 | 128 |
| 2010 | 0.6 | 128 |
| 2009 | 0.6 | 127 |
| 2008 | 0.6 | 129 |
| 2005 | 0.3 | 137 |
| 2004 | 0.3 | 136 |
| 2003 | 0.3 | 135 |
| 1995 | 0.3 | 118 |
| 1994 | 0.3 | 121 |
| 1993 | 0.5 | 102 |
| 1992 | 0.5 | 95 |
| 1991 | 0.5 | 95 |
| 1990 | 0.5 | 94 |
| 1989 | 0.4 | 91 |
| 1988 | 0.4 | 90 |
| 1987 | 0.4 | 87 |
| 1986 | 0.3 | 88 |