| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.91 | 98 |
| 2015 | 6.19 | 78 |
| 2014 | 7.35 | 100 |
| 2013 | 8.63 | 111 |
| 2012 | 10.02 | 123 |
| 2011 | 12.33 | 138 |
| 2010 | 16.71 | 162 |
| 2009 | 13.55 | 152 |
| 2008 | 5.45 | 65 |
| 2007 | 4.59 | 51 |
| 2006 | 5.91 | 66 |
| 2005 | 8.03 | 102 |
| 2004 | 10.25 | 123 |
| 2003 | 11.29 | 129 |
| 2002 | 10.03 | 118 |
| 2001 | 13.14 | 144 |
| 2000 | 13.36 | 141 |
| 1999 | 11.57 | 123 |
| 1998 | 9.51 | 112 |
| 1997 | 10.37 | 120 |
| 1996 | 9.91 | 113 |
| 1995 | 9.66 | 118 |
| 1994 | 7.56 | 88 |
| 1993 | 6.54 | 76 |
| 1992 | 3.68 | 38 |
| 1991 | 1.47 | 11 |