| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2015 | 7.87 | 23 |
| 2014 | 8.37 | 15 |
| 2013 | 9.04 | 15 |
| 2012 | 9.45 | 26 |
| 2011 | 9.27 | 36 |
| 2010 | 9.32 | 20 |
| 2009 | 11.08 | 18 |
| 2008 | 9.88 | 78 |
| 2007 | 5.75 | 79 |
| 2006 | 6.92 | 59 |
| 2005 | 6.84 | 63 |
| 2004 | 2.84 | 102 |
| 2003 | 5.71 | 60 |
| 2002 | 3.03 | 88 |
| 2001 | 2.69 | 113 |
| 2000 | 2.48 | 106 |
| 1999 | 7.45 | 45 |
| 1998 | 11.24 | 39 |
| 1997 | 4.01 | 96 |
| 1996 | 9.22 | 66 |
| 1995 | 7.62 | 96 |
| 1994 | 8.35 | 87 |
| 1993 | 7.51 | 77 |
| 1992 | 17.15 | 39 |
| 1991 | 15.56 | 48 |
| 1990 | 8.24 | 69 |
| 1989 | 8.85 | 59 |
| 1988 | 8.98 | 55 |
| 1987 | 10.75 | 47 |
| 1986 | 19 | 28 |