| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 8.65 | 67 |
| 2015 | 8.45 | 82 |
| 2014 | 8.87 | 83 |
| 2013 | 9.11 | 85 |
| 2012 | 9.79 | 75 |
| 2011 | 11.45 | 69 |
| 2010 | 10.09 | 79 |
| 2009 | 9.22 | 85 |
| 2008 | 9.97 | 80 |
| 2007 | 9.99 | 78 |
| 2006 | 8.61 | 92 |
| 2005 | 8.26 | 94 |
| 2004 | 9.27 | 94 |
| 2003 | 9.31 | 91 |
| 2002 | 8.98 | 91 |
| 2001 | 8.01 | 99 |
| 2000 | 8.6 | 95 |
| 1999 | 10.84 | 84 |
| 1998 | 13.31 | 79 |
| 1997 | 11.1 | 85 |
| 1996 | 11.68 | 87 |
| 1995 | 12.95 | 82 |
| 1994 | 13.66 | 76 |
| 1993 | 13.79 | 75 |
| 1992 | 14.57 | 73 |
| 1991 | 14.36 | 72 |
| 1990 | 15.22 | 74 |
| 1989 | 18.08 | 56 |
| 1988 | 20.07 | 51 |
| 1987 | 19.96 | 53 |
| 1986 | 20.18 | 50 |