| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.35 | 86 |
| 2015 | 9.09 | 74 |
| 2014 | 7.87 | 97 |
| 2013 | 9.55 | 83 |
| 2012 | 9.36 | 88 |
| 2011 | 7.23 | 105 |
| 2010 | 9.06 | 106 |
| 2009 | 11.35 | 78 |
| 2008 | 8.52 | 119 |
| 2007 | 10.29 | 136 |
| 2006 | 12.99 | 114 |
| 2005 | 13.72 | 91 |
| 2004 | 10.81 | 97 |
| 2003 | 45.15 | 11 |
| 2002 | 8.29 | 101 |
| 2001 | 36.89 | 30 |
| 2000 | 21.45 | 46 |
| 1999 | 8.71 | 111 |
| 1998 | 19.48 | 36 |
| 1997 | 25.36 | 40 |
| 1996 | 5.73 | 129 |
| 1995 | 15.56 | 77 |
| 1994 | 3.83 | 133 |
| 1993 | 6.28 | 101 |
| 1992 | 20.62 | 53 |
| 1991 | 48.53 | 17 |
| 1990 | 22.15 | 41 |
| 1989 | 16.34 | 65 |
| 1988 | 19.73 | 58 |
| 1987 | 8.33 | 90 |
| 1986 | 20.74 | 41 |