| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 7.6 | 30 |
| 2015 | 7.4 | 33 |
| 2014 | 6.5 | 42 |
| 2013 | 6.2 | 40 |
| 2012 | 4.2 | 45 |
| 2011 | 3.4 | 49 |
| 2010 | 4 | 51 |
| 2009 | 4.2 | 49 |
| 2008 | 6.4 | 50 |
| 2007 | 9.1 | 49 |
| 2006 | 5.2 | 53 |
| 2005 | 3.7 | 49 |
| 2004 | 3.1 | 50 |
| 2003 | 3.7 | 44 |
| 2002 | 2.5 | 46 |
| 2001 | 20.6 | 27 |
| 2000 | 14.7 | 32 |
| 1999 | 45.6 | 19 |
| 1998 | 47.8 | 11 |
| 1997 | 19.3 | 27 |
| 1996 | 15.5 | 23 |
| 1995 | 19.3 | 18 |