| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 8.8 | 91 |
| 2015 | 8.58 | 91 |
| 2014 | 8.42 | 91 |
| 2013 | 8.29 | 92 |
| 2012 | 8.19 | 92 |
| 2011 | 8.1 | 90 |
| 2010 | 7.99 | 90 |
| 2009 | 7.93 | 90 |
| 2008 | 7.87 | 91 |
| 2007 | 7.8 | 88 |
| 2006 | 7.73 | 86 |
| 2005 | 7.64 | 86 |
| 2004 | 7.58 | 88 |
| 2003 | 7.51 | 87 |
| 2002 | 7.43 | 86 |
| 2001 | 7.33 | 84 |
| 2000 | 7.23 | 84 |
| 1999 | 7.17 | 81 |
| 1998 | 7.1 | 82 |
| 1997 | 7.03 | 79 |
| 1996 | 6.95 | 78 |
| 1995 | 6.85 | 76 |
| 1994 | 6.82 | 72 |
| 1993 | 6.77 | 71 |
| 1992 | 6.72 | 71 |
| 1991 | 6.65 | 72 |
| 1990 | 6.57 | 71 |
| 1989 | 6.58 | 70 |
| 1988 | 6.58 | 73 |
| 1987 | 6.56 | 73 |
| 1986 | 6.53 | 71 |