| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.3 | 22 |
| 2015 | 6.58 | 30 |
| 2014 | 6.88 | 29 |
| 2013 | 5.72 | 48 |
| 2012 | 9.38 | 27 |
| 2011 | 14.02 | 17 |
| 2010 | 3.96 | 80 |
| 2009 | 9.23 | 26 |
| 2008 | 26.24 | 7 |
| 2007 | 9.76 | 27 |
| 2006 | 14.45 | 6 |
| 2005 | 10.31 | 32 |
| 2004 | 11.62 | 24 |
| 2003 | 9.82 | 35 |
| 2002 | 1.96 | 119 |
| 2001 | 5.74 | 58 |
| 2000 | 9.98 | 34 |
| 1999 | 5.74 | 59 |
| 1998 | 6.72 | 68 |
| 1997 | 11.36 | 41 |
| 1996 | 8.86 | 68 |
| 1995 | 1.55 | 151 |
| 1994 | 28.81 | 45 |
| 1993 | 45.98 | 25 |
| 1992 | 27.33 | 27 |
| 1991 | 20.08 | 39 |
| 1990 | 17.78 | 37 |
| 1989 | 13.79 | 41 |
| 1988 | 12.26 | 45 |
| 1987 | 8.64 | 55 |
| 1986 | 2.53 | 89 |