| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 7.66 | 7 |
| 2015 | 7.47 | 5 |
| 2014 | 7.69 | 8 |
| 2013 | 6.71 | 18 |
| 2012 | 8.19 | 16 |
| 2011 | 11.46 | 8 |
| 2010 | 9.42 | 11 |
| 2009 | 10.6 | 5 |
| 2008 | 8.29 | 18 |
| 2007 | 12.58 | 18 |
| 2006 | 8.92 | 24 |
| 2005 | 11.14 | 14 |
| 2004 | 8.23 | 26 |
| 2003 | 6.71 | 29 |
| 2002 | 9.88 | 15 |
| 2001 | 7.55 | 16 |
| 2000 | 12.52 | 7 |
| 1999 | 11.92 | 3 |
| 1998 | 8.23 | 16 |
| 1997 | 6.37 | 21 |
| 1996 | 14.25 | 8 |
| 1995 | 13.8 | 8 |
| 1994 | 10.14 | 6 |
| 1993 | 17.67 | 1 |
| 1992 | 17.07 | 3 |
| 1991 | 12.41 | 8 |