| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 13.33 | 35 |
| 2015 | 9.2 | 72 |
| 2014 | 12.44 | 53 |
| 2013 | 29.33 | 4 |
| 2012 | 6.98 | 106 |
| 2011 | 5.31 | 123 |
| 2010 | 10.9 | 93 |
| 2009 | 8.64 | 90 |
| 2008 | 10.04 | 110 |
| 2007 | 9.61 | 140 |
| 2006 | 32.92 | 30 |
| 2005 | 6.43 | 140 |
| 2004 | 9.92 | 105 |
| 2003 | 3.6 | 135 |
| 2002 | 10.4 | 88 |
| 2001 | 3.58 | 143 |
| 2000 | 8.12 | 113 |
| 1999 | 16.88 | 60 |
| 1998 | 8.57 | 93 |
| 1997 | 23.11 | 54 |
| 1996 | 23.73 | 48 |
| 1995 | 23.87 | 52 |
| 1994 | 26.73 | 58 |
| 1993 | 28.15 | 41 |
| 1992 | 13.11 | 79 |
| 1991 | 17.72 | 62 |
| 1990 | 22.4 | 40 |
| 1989 | 30.24 | 33 |
| 1988 | 23.26 | 40 |
| 1987 | 11.67 | 75 |
| 1986 | 1.69 | 109 |