| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.96 | 10 |
| 2015 | 6.96 | 13 |
| 2014 | 6.97 | 21 |
| 2013 | 7.26 | 22 |
| 2012 | 5.14 | 56 |
| 2011 | 7.9 | 26 |
| 2010 | 6.36 | 62 |
| 2009 | 5.38 | 28 |
| 2008 | 5.57 | 74 |
| 2007 | 8.46 | 45 |
| 2006 | 4.66 | 129 |
| 2005 | 8.17 | 34 |
| 2004 | 7.83 | 41 |
| 2003 | 6.89 | 48 |
| 2002 | 7.16 | 21 |
| 2001 | 6 | 34 |
| 2000 | 4.93 | 79 |
| 1999 | 4.84 | 51 |
| 1998 | 3.71 | 104 |
| 1997 | 3.53 | 118 |
| 1996 | 4.54 | 87 |
| 1995 | 3.57 | 107 |
| 1994 | 1.57 | 134 |
| 1993 | 1.21 | 115 |
| 1992 | 0.58 | 116 |
| 1991 | 2.07 | 91 |
| 1990 | 7.05 | 27 |
| 1989 | 3.76 | 88 |