| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.12 | 2 |
| 2015 | 6.36 | 6 |
| 2014 | 6.76 | 7 |
| 2013 | 7.23 | 12 |
| 2012 | 7.33 | 13 |
| 2011 | 9.01 | 11 |
| 2010 | 10.1 | 5 |
| 2009 | 8.86 | 4 |
| 2008 | 9.09 | 8 |
| 2007 | 13.64 | 7 |
| 2006 | 12.09 | 9 |
| 2005 | 10.74 | 13 |
| 2004 | 9.46 | 15 |
| 2003 | 9.35 | 14 |
| 2002 | 8.4 | 9 |
| 2001 | 7.56 | 14 |
| 2000 | 7.64 | 18 |
| 1999 | 6.74 | 21 |
| 1998 | 6.81 | 20 |
| 1997 | 8.12 | 18 |
| 1996 | 8.78 | 11 |
| 1995 | 9.75 | 7 |
| 1994 | 11.78 | 5 |
| 1993 | 12.57 | 4 |
| 1992 | 12.82 | 3 |
| 1991 | 7.81 | 9 |
| 1990 | 2.39 | 66 |
| 1989 | 2.6 | 66 |
| 1988 | 9.46 | 16 |
| 1987 | 9.91 | 8 |
| 1986 | 7.33 | 15 |