| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 1 | 45 |
| 2015 | 0.9 | 46 |
| 2014 | 2.1 | 52 |
| 2013 | 1.8 | 53 |
| 2012 | 0.9 | 63 |
| 2011 | 0.5 | 71 |
| 2010 | 1.1 | 62 |
| 2009 | 2 | 60 |
| 2008 | 8.1 | 43 |
| 2007 | 4.8 | 57 |
| 2006 | 7.5 | 49 |
| 2005 | 4.4 | 47 |
| 2004 | 2.4 | 54 |
| 2003 | 2.4 | 50 |
| 2001 | 2.1 | 52 |
| 2000 | 2.7 | 54 |
| 1999 | 6.7 | 40 |
| 1998 | 9.3 | 39 |
| 1997 | 7.6 | 43 |
| 1996 | 2.9 | 47 |
| 1995 | 1.8 | 48 |
| 1994 | 2.9 | 44 |