| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 19.1 | 96 |
| 2015 | 18.8 | 111 |
| 2014 | 18.5 | 113 |
| 2013 | 17.9 | 115 |
| 2012 | 17.8 | 117 |
| 2011 | 17.4 | 117 |
| 2010 | 17.2 | 122 |
| 2009 | 17.9 | 107 |
| 2008 | 17.8 | 106 |
| 2007 | 16.2 | 106 |
| 2006 | 15.6 | 105 |
| 2005 | 14.8 | 101 |
| 2004 | 14.7 | 100 |
| 2003 | 14.8 | 96 |
| 2002 | 17.2 | 95 |
| 2001 | 20.4 | 87 |
| 2000 | 15.1 | 94 |
| 1999 | 15.5 | 90 |
| 1998 | 14.8 | 92 |
| 1997 | 14.3 | 92 |
| 1996 | 14.6 | 92 |
| 1995 | 14.6 | 91 |
| 1994 | 13.8 | 87 |
| 1993 | 14 | 85 |
| 1992 | 14.6 | 80 |
| 1991 | 16.3 | 75 |
| 1990 | 16.3 | 72 |