| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 38.1 | 90 |
| 2014 | 34.8 | 90 |
| 2013 | 33.2 | 94 |
| 2012 | 31.8 | 94 |
| 2011 | 30.8 | 93 |
| 2010 | 28.8 | 98 |
| 2009 | 28.5 | 95 |
| 2008 | 27.5 | 92 |
| 2007 | 24.9 | 92 |
| 2006 | 20.9 | 97 |
| 2005 | 18.9 | 96 |
| 2004 | 20.1 | 94 |
| 2003 | 19.1 | 91 |
| 2002 | 18.5 | 93 |
| 2001 | 19 | 92 |
| 2000 | 18.5 | 91 |
| 1999 | 18.2 | 88 |
| 1998 | 17.5 | 88 |
| 1997 | 16.9 | 90 |
| 1996 | 16.3 | 89 |
| 1995 | 15.9 | 89 |
| 1994 | 15.5 | 84 |
| 1993 | 15.2 | 82 |
| 1992 | 15.1 | 77 |
| 1991 | 14.2 | 80 |
| 1990 | 12.7 | 81 |
| 1989 | 12 | 70 |
| 1988 | 12.2 | 67 |
| 1987 | 11.8 | 68 |
| 1986 | 11.8 | 67 |