| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.3 | 34 |
| 2015 | 9.2 | 27 |
| 2014 | 14 | 30 |
| 2013 | 10 | 36 |
| 2012 | 6.1 | 39 |
| 2011 | 8 | 39 |
| 2010 | 13.6 | 36 |
| 2009 | 18 | 35 |
| 2008 | 23.1 | 32 |
| 2007 | 38.2 | 31 |
| 2006 | 31.7 | 30 |
| 2005 | 19.8 | 27 |
| 2004 | 16.6 | 34 |
| 2003 | 16.8 | 29 |
| 2002 | 13.3 | 30 |
| 2001 | 27.3 | 23 |
| 2000 | 70.4 | 16 |
| 1999 | 129 | 6 |
| 1998 | 34.6 | 22 |
| 1997 | 14.8 | 31 |
| 1996 | 5.6 | 38 |
| 1995 | 4.3 | 40 |
| 1994 | 4.3 | 40 |
| 1993 | 4.6 | 36 |
| 1992 | 2.4 | 30 |
| 1991 | 4.6 | 26 |
| 1990 | 8.1 | 20 |
| 1989 | 1.8 | 30 |
| 1988 | 1.1 | 32 |
| 1987 | 1.8 | 29 |
| 1986 | 0.2 | 32 |