| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.79 | 67 |
| 2015 | 6.62 | 67 |
| 2014 | 6.59 | 67 |
| 2013 | 6.63 | 68 |
| 2012 | 6.7 | 70 |
| 2011 | 6.79 | 72 |
| 2010 | 6.9 | 75 |
| 2009 | 7.25 | 78 |
| 2008 | 7.66 | 87 |
| 2007 | 8.12 | 94 |
| 2006 | 8.56 | 96 |
| 2005 | 8.9 | 99 |
| 2004 | 9.22 | 105 |
| 2003 | 9.37 | 107 |
| 2002 | 9.36 | 110 |
| 2001 | 9.3 | 112 |
| 2000 | 9.25 | 112 |
| 1999 | 9.31 | 115 |
| 1998 | 9.42 | 118 |
| 1997 | 9.57 | 120 |
| 1996 | 9.65 | 123 |
| 1995 | 9.62 | 122 |
| 1994 | 9.62 | 122 |
| 1993 | 9.47 | 121 |
| 1992 | 9.22 | 121 |
| 1991 | 8.96 | 122 |
| 1990 | 8.74 | 121 |
| 1989 | 8.66 | 122 |
| 1988 | 8.67 | 122 |
| 1987 | 8.74 | 122 |
| 1986 | 8.85 | 122 |