| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 7.11 | 8 |
| 2015 | 8.01 | 6 |
| 2014 | 7.51 | 14 |
| 2013 | 6.39 | 31 |
| 2012 | 5.46 | 49 |
| 2011 | 6.64 | 41 |
| 2010 | 10.26 | 13 |
| 2009 | 8.48 | 12 |
| 2008 | 3.89 | 97 |
| 2007 | 9.8 | 28 |
| 2006 | 9.26 | 29 |
| 2005 | 9.28 | 24 |
| 2004 | 7.92 | 40 |
| 2003 | 7.86 | 32 |
| 2002 | 3.8 | 86 |
| 2001 | 4.82 | 52 |
| 2000 | 3.84 | 114 |
| 1999 | 8.85 | 16 |
| 1998 | 6.18 | 41 |
| 1997 | 4.05 | 105 |
| 1996 | 7.55 | 32 |
| 1995 | 7.57 | 26 |
| 1994 | 6.66 | 37 |
| 1993 | 4.75 | 56 |
| 1992 | 5.48 | 50 |
| 1991 | 1.06 | 108 |
| 1990 | 5.53 | 47 |
| 1989 | 5.95 | 41 |
| 1988 | 9.63 | 20 |
| 1987 | 3.97 | 69 |
| 1986 | 4.78 | 58 |