| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 2.8 | 50 |
| 2015 | 2.6 | 50 |
| 2014 | 4.1 | 52 |
| 2013 | 3.9 | 50 |
| 2012 | 5.1 | 48 |
| 2011 | 6.3 | 58 |
| 2010 | 3.9 | 64 |
| 2009 | 4.1 | 59 |
| 2008 | 9.7 | 59 |
| 2007 | 11.6 | 52 |
| 2006 | 10.3 | 50 |
| 2005 | 7.1 | 52 |
| 2004 | 5.8 | 56 |
| 2003 | 6.9 | 51 |
| 2002 | 8.4 | 42 |
| 2001 | 7.5 | 50 |
| 2000 | 22.5 | 37 |
| 1999 | 20.3 | 40 |
| 1998 | 26.6 | 41 |
| 1997 | 24.9 | 36 |