| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 25.4 | 55 |
| 2014 | 33.1 | 50 |
| 2013 | 32.3 | 52 |
| 2012 | 31.9 | 51 |
| 2011 | 34.1 | 47 |
| 2010 | 32.2 | 48 |
| 2009 | 33.3 | 44 |
| 2008 | 37.5 | 41 |
| 2007 | 35 | 41 |
| 2006 | 26.4 | 43 |
| 2005 | 26.9 | 40 |
| 2004 | 26.8 | 39 |
| 2003 | 23.8 | 38 |
| 2002 | 18.8 | 38 |
| 2001 | 17.9 | 42 |
| 2000 | 19.3 | 38 |
| 1999 | 21.2 | 36 |
| 1998 | 21.6 | 36 |
| 1997 | 21.6 | 39 |
| 1996 | 24.6 | 36 |
| 1995 | 25.6 | 34 |
| 1994 | 22.3 | 34 |
| 1993 | 21.2 | 34 |
| 1992 | 21.4 | 32 |
| 1991 | 19.9 | 32 |
| 1990 | 19.7 | 31 |
| 1989 | 16.2 | 33 |
| 1988 | 17.1 | 31 |