| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 21.1 | 31 |
| 2015 | 16.4 | 32 |
| 2014 | 11.6 | 44 |
| 2013 | 8.8 | 44 |
| 2012 | 8.6 | 44 |
| 2011 | 7.5 | 55 |
| 2010 | 14.7 | 45 |
| 2009 | 16.1 | 44 |
| 2008 | 35.5 | 41 |
| 2007 | 17.1 | 47 |
| 2006 | 7.4 | 52 |
| 2005 | 6.8 | 53 |
| 2004 | 5.2 | 59 |
| 2003 | 7.2 | 48 |
| 2002 | 5.2 | 48 |
| 2001 | 29.9 | 31 |
| 2000 | 18 | 41 |
| 1999 | 65.5 | 9 |
| 1998 | 61.9 | 17 |
| 1997 | 32.7 | 32 |