| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2014 | 0.2 | 67 |
| 2013 | 0.2 | 72 |
| 2012 | 5.3 | 42 |
| 2011 | 4.5 | 44 |
| 2010 | 6.6 | 44 |
| 2009 | 10.5 | 41 |
| 2008 | 24.9 | 31 |
| 2007 | 65.5 | 23 |
| 2006 | 90.9 | 13 |
| 2005 | 127.3 | 6 |
| 2004 | 143.2 | 4 |
| 2001 | 17.2 | 28 |
| 2000 | 41.9 | 25 |
| 1999 | 33.1 | 22 |
| 1998 | 14.5 | 32 |
| 1997 | 16.9 | 29 |
| 1996 | 8.8 | 31 |
| 1995 | 0.3 | 66 |
| 1994 | 0.1 | 68 |
| 1993 | 0.1 | 58 |