| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.4 | 61 |
| 2015 | 6.22 | 56 |
| 2014 | 6.14 | 55 |
| 2013 | 6.1 | 55 |
| 2012 | 6.1 | 54 |
| 2011 | 6.15 | 59 |
| 2010 | 6.24 | 61 |
| 2009 | 6.42 | 65 |
| 2008 | 6.65 | 70 |
| 2007 | 6.91 | 72 |
| 2006 | 7.15 | 78 |
| 2005 | 7.31 | 79 |
| 2004 | 7.43 | 84 |
| 2003 | 7.45 | 86 |
| 2002 | 7.37 | 84 |
| 2001 | 7.28 | 83 |
| 2000 | 7.2 | 83 |
| 1999 | 7.2 | 83 |
| 1998 | 7.24 | 83 |
| 1997 | 7.29 | 84 |
| 1996 | 7.31 | 84 |
| 1995 | 7.27 | 85 |
| 1994 | 7.23 | 85 |
| 1993 | 7.14 | 84 |
| 1992 | 7.01 | 79 |
| 1991 | 6.88 | 78 |
| 1990 | 6.78 | 77 |
| 1989 | 6.75 | 78 |
| 1988 | 6.76 | 80 |
| 1987 | 6.81 | 82 |
| 1986 | 6.89 | 82 |