| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2015 | 8.7 | 29 |
| 2014 | 10.77 | 16 |
| 2013 | 12.91 | 15 |
| 2012 | 9.05 | 31 |
| 2011 | 17.29 | 13 |
| 2010 | 9.32 | 29 |
| 2009 | 7.35 | 45 |
| 2008 | 8.59 | 47 |
| 2007 | 7.58 | 70 |
| 2006 | 4.33 | 92 |
| 2005 | 4.73 | 72 |
| 2004 | 4.4 | 60 |
| 2003 | 3.05 | 75 |
| 2002 | 2.76 | 89 |
| 2001 | 2.36 | 90 |
| 2000 | 3.57 | 80 |
| 1999 | 2.09 | 95 |
| 1998 | 2.13 | 101 |
| 1997 | 2.24 | 84 |
| 1996 | 2.07 | 67 |
| 1995 | 1.81 | 70 |
| 1994 | 2.46 | 44 |
| 1993 | 2.14 | 39 |
| 1992 | 2.32 | 36 |
| 1991 | 2.66 | 33 |
| 1990 | 2.6 | 33 |
| 1989 | 2.32 | 33 |
| 1988 | 0.71 | 59 |
| 1987 | 3.61 | 16 |
| 1986 | 3.81 | 12 |