| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 9.7 | 29 |
| 2015 | 8.7 | 29 |
| 2014 | 10.2 | 35 |
| 2013 | 10.8 | 32 |
| 2012 | 10 | 34 |
| 2011 | 11.8 | 34 |
| 2010 | 13.8 | 35 |
| 2009 | 16 | 36 |
| 2008 | 14.9 | 38 |
| 2007 | 22 | 37 |
| 2006 | 11.1 | 41 |
| 2005 | 9.7 | 40 |
| 2004 | 8.5 | 40 |
| 2003 | 5.4 | 39 |
| 2002 | 6.3 | 35 |
| 2001 | 6 | 38 |
| 2000 | 7.8 | 38 |
| 1999 | 15.1 | 36 |
| 1998 | 13.5 | 34 |
| 1997 | 10.2 | 38 |
| 1996 | 14.3 | 24 |
| 1995 | 7.1 | 35 |
| 1994 | 6.7 | 34 |
| 1993 | 5.8 | 33 |