| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.84 | 68 |
| 2015 | 6.95 | 69 |
| 2014 | 7.21 | 76 |
| 2013 | 7.57 | 83 |
| 2012 | 8.02 | 90 |
| 2011 | 8.5 | 95 |
| 2010 | 8.95 | 99 |
| 2009 | 9.24 | 102 |
| 2008 | 9.51 | 107 |
| 2007 | 9.77 | 111 |
| 2006 | 9.99 | 114 |
| 2005 | 10.17 | 116 |
| 2004 | 10.2 | 120 |
| 2003 | 10.15 | 119 |
| 2002 | 10.04 | 118 |
| 2001 | 9.91 | 119 |
| 2000 | 9.78 | 119 |
| 1999 | 9.64 | 120 |
| 1998 | 9.53 | 119 |
| 1997 | 9.42 | 119 |
| 1996 | 9.3 | 117 |
| 1995 | 9.15 | 117 |
| 1994 | 9.05 | 117 |
| 1993 | 8.93 | 117 |
| 1992 | 8.79 | 118 |
| 1991 | 8.7 | 119 |
| 1990 | 8.7 | 120 |
| 1989 | 8.66 | 121 |
| 1988 | 8.75 | 123 |
| 1987 | 8.92 | 124 |
| 1986 | 9.12 | 127 |