| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.18 | 81 |
| 2015 | 7.5 | 103 |
| 2014 | 8.99 | 117 |
| 2013 | 10.33 | 128 |
| 2012 | 10.09 | 124 |
| 2011 | 9.63 | 123 |
| 2010 | 9.64 | 126 |
| 2009 | 8.17 | 101 |
| 2008 | 7.12 | 102 |
| 2007 | 9.6 | 138 |
| 2006 | 13.84 | 154 |
| 2005 | 17.75 | 166 |
| 2004 | 19.07 | 168 |
| 2003 | 19.37 | 168 |
| 2002 | 19.9 | 172 |
| 2001 | 18.37 | 166 |
| 2000 | 16.31 | 163 |
| 1999 | 12.29 | 133 |
| 1998 | 9.94 | 116 |
| 1997 | 10.96 | 126 |
| 1996 | 12.35 | 133 |
| 1995 | 13.34 | 143 |
| 1994 | 14.44 | 143 |
| 1993 | 14 | 143 |
| 1992 | 13.32 | 139 |
| 1991 | 11.97 | 134 |