| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 13.81 | 9 |
| 2015 | 10.36 | 12 |
| 2014 | 10.15 | 10 |
| 2013 | 9.42 | 13 |
| 2012 | 7.12 | 41 |
| 2011 | 10.05 | 29 |
| 2010 | 11.27 | 12 |
| 2009 | 11.76 | 14 |
| 2008 | 18.32 | 23 |
| 2007 | 9.32 | 29 |
| 2006 | 7.64 | 48 |
| 2005 | 4.87 | 80 |
| 2004 | 11.27 | 26 |
| 2003 | 4.51 | 72 |
| 2002 | 2.74 | 95 |
| 2001 | 2.27 | 126 |
| 2000 | 2.68 | 101 |
| 1999 | 3.08 | 84 |
| 1998 | 3.87 | 95 |
| 1997 | 4.63 | 89 |
| 1996 | 7.19 | 80 |
| 1995 | 15.74 | 55 |
| 1994 | 8.15 | 90 |
| 1993 | 12.09 | 55 |
| 1992 | 13.64 | 49 |
| 1991 | 19.75 | 40 |
| 1990 | 16.76 | 42 |
| 1989 | 21.26 | 27 |
| 1988 | 17.66 | 33 |
| 1987 | 19.69 | 29 |
| 1986 | 23.86 | 22 |