| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2014 | 20.4 | 26 |
| 2013 | 17.2 | 27 |
| 2012 | 12.2 | 30 |
| 2011 | 14.6 | 28 |
| 2010 | 22.5 | 28 |
| 2009 | 18.4 | 34 |
| 2008 | 29 | 29 |
| 2007 | 57.2 | 24 |
| 2006 | 31.7 | 31 |
| 2005 | 18.1 | 32 |
| 2004 | 19.6 | 32 |
| 2003 | 14.5 | 30 |
| 2002 | 16.8 | 26 |
| 2001 | 22.4 | 26 |
| 2000 | 47 | 24 |
| 1999 | 29.9 | 25 |
| 1998 | 40.5 | 14 |
| 1997 | 17 | 28 |
| 1996 | 5.8 | 37 |
| 1995 | 3.6 | 42 |
| 1994 | 5 | 37 |
| 1993 | 2.5 | 41 |