| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 27.5 | 47 |
| 2015 | 25.8 | 53 |
| 2014 | 26.9 | 55 |
| 2013 | 24.5 | 57 |
| 2012 | 21 | 60 |
| 2011 | 23.8 | 56 |
| 2010 | 20.9 | 55 |
| 2009 | 22.3 | 53 |
| 2008 | 30 | 49 |
| 2007 | 26.1 | 47 |
| 2006 | 22.5 | 47 |
| 2005 | 19.8 | 48 |
| 2004 | 15.3 | 48 |
| 2003 | 12.5 | 52 |
| 2002 | 10.6 | 52 |
| 2001 | 9.9 | 50 |
| 2000 | 9.4 | 51 |
| 1999 | 9.6 | 53 |
| 1998 | 12.5 | 48 |
| 1997 | 10.7 | 53 |
| 1996 | 8.7 | 51 |
| 1995 | 9.8 | 52 |
| 1994 | 9.4 | 50 |
| 1993 | 7.2 | 53 |
| 1992 | 10.7 | 45 |
| 1991 | 13.8 | 40 |
| 1990 | 17.7 | 35 |
| 1989 | 20.2 | 28 |
| 1988 | 17.2 | 30 |
| 1987 | 15 | 31 |