| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 3.28 | 3 |
| 2015 | 2.12 | 22 |
| 2014 | 1.12 | 67 |
| 2013 | 0.74 | 91 |
| 2012 | 1.32 | 60 |
| 2011 | 2.62 | 18 |
| 2010 | 4.3 | 5 |
| 2009 | 5.85 | 2 |
| 2008 | 7.09 | 2 |
| 2007 | 7.58 | 2 |
| 2006 | 7.34 | 2 |
| 2005 | 6.78 | 3 |
| 2004 | 6.28 | 3 |
| 2003 | 5.7 | 2 |
| 2002 | 5.24 | 2 |
| 2001 | 4.86 | 2 |
| 2000 | 4.35 | 4 |
| 1999 | 3.68 | 7 |
| 1998 | 3.13 | 14 |
| 1997 | 2.8 | 20 |
| 1996 | 2.65 | 24 |
| 1995 | 2.57 | 29 |
| 1994 | 2.49 | 33 |
| 1993 | 2.5 | 36 |
| 1992 | 1.99 | 52 |
| 1991 | 1.15 | 91 |
| 1990 | 1.44 | 70 |
| 1989 | 1.75 | 67 |
| 1988 | 1.96 | 56 |
| 1987 | 1.92 | 57 |
| 1986 | 1.71 | 69 |