| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.56 | 86 |
| 2015 | 6.62 | 84 |
| 2014 | 7.27 | 99 |
| 2013 | 7.1 | 95 |
| 2012 | 7.22 | 94 |
| 2011 | 7.18 | 93 |
| 2010 | 7.71 | 96 |
| 2009 | 8.65 | 111 |
| 2008 | 7.84 | 118 |
| 2007 | 8.41 | 118 |
| 2006 | 9.45 | 129 |
| 2005 | 11.51 | 144 |
| 2004 | 13.52 | 150 |
| 2003 | 16.03 | 157 |
| 2002 | 19.6 | 171 |
| 2001 | 17.4 | 164 |
| 2000 | 15.02 | 154 |
| 1999 | 14.1 | 150 |
| 1998 | 12.8 | 138 |
| 1997 | 14.9 | 154 |
| 1996 | 17.2 | 162 |
| 1995 | 18.8 | 167 |
| 1994 | 12.1 | 132 |
| 1993 | 10.1 | 117 |
| 1992 | 6.7 | 81 |
| 1991 | 5.8 | 67 |