| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 3.3 | 29 |
| 2015 | 3.1 | 27 |
| 2014 | 2.87 | 22 |
| 2013 | 3.1 | 24 |
| 2012 | 3 | 23 |
| 2011 | 3.1 | 21 |
| 2010 | 3.4 | 26 |
| 2009 | 3.7 | 31 |
| 2008 | 3.3 | 33 |
| 2007 | 3.2 | 30 |
| 2006 | 3.3 | 28 |
| 2005 | 3.5 | 27 |
| 2004 | 3.5 | 27 |
| 2003 | 3.6 | 26 |
| 2002 | 3.5 | 31 |
| 2001 | 3.5 | 29 |
| 2000 | 3 | 26 |
| 1999 | 3.4 | 30 |
| 1998 | 3.2 | 26 |
| 1997 | 2.4 | 18 |
| 1996 | 2.5 | 19 |
| 1995 | 3.1 | 25 |
| 1994 | 3.77 | 37 |
| 1993 | 4.1 | 44 |
| 1992 | 3.7 | 39 |
| 1991 | 3.25 | 39 |