| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 3.75 | 35 |
| 2015 | 2.54 | 72 |
| 2014 | 7.19 | 26 |
| 2013 | 7.69 | 25 |
| 2012 | 9.69 | 25 |
| 2011 | 11.92 | 23 |
| 2010 | 13.88 | 5 |
| 2009 | 13.65 | 7 |
| 2008 | 20.29 | 19 |
| 2007 | 7.6 | 58 |
| 2006 | 7.92 | 47 |
| 2005 | 9.06 | 40 |
| 2004 | 7.44 | 47 |
| 2003 | 2.91 | 95 |
| 2002 | 3.29 | 82 |
| 2001 | 3.15 | 102 |
| 2000 | 4.37 | 67 |
| 1999 | 4.14 | 70 |
| 1998 | 6.23 | 73 |
| 1997 | 11.38 | 40 |
| 1996 | 10.37 | 59 |
| 1995 | 12.34 | 62 |
| 1994 | 12.37 | 70 |
| 1993 | 9.97 | 67 |
| 1992 | 9.51 | 64 |
| 1991 | 11.79 | 61 |
| 1990 | 9.05 | 64 |
| 1989 | 7.84 | 63 |
| 1988 | 8.84 | 56 |
| 1987 | 4.68 | 73 |
| 1986 | 3.51 | 80 |