| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 7.85 | 15 |
| 2015 | 4.95 | 42 |
| 2014 | 5.69 | 43 |
| 2013 | 5.62 | 51 |
| 2012 | 8.94 | 32 |
| 2011 | 6.11 | 67 |
| 2010 | 4.51 | 71 |
| 2009 | 7.45 | 34 |
| 2008 | 12.66 | 45 |
| 2007 | 8.08 | 49 |
| 2006 | 5.3 | 80 |
| 2005 | 4.77 | 82 |
| 2004 | 3.45 | 92 |
| 2003 | 7.29 | 49 |
| 2002 | 12.02 | 27 |
| 2001 | 5.94 | 56 |
| 2000 | 12.21 | 26 |
| 1999 | 6.09 | 55 |
| 1998 | 8.11 | 54 |
| 1997 | 7.13 | 69 |
| 1996 | 6.43 | 86 |
| 1995 | 12.29 | 63 |
| 1994 | 13.77 | 66 |
| 1993 | 12.02 | 56 |
| 1992 | 7.56 | 73 |
| 1991 | 8.93 | 74 |
| 1990 | 13.09 | 50 |
| 1989 | 7.55 | 68 |
| 1988 | 20.39 | 30 |
| 1987 | 13.38 | 39 |
| 1986 | 13.74 | 40 |