| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 9.7 | 28 |
| 2015 | 8.1 | 32 |
| 2014 | 10.4 | 34 |
| 2013 | 14.8 | 29 |
| 2012 | 17.4 | 26 |
| 2011 | 20.3 | 26 |
| 2010 | 26.5 | 27 |
| 2009 | 21.5 | 31 |
| 2008 | 16.1 | 36 |
| 2007 | 26 | 36 |
| 2006 | 18 | 37 |
| 2005 | 16.6 | 34 |
| 2004 | 13.2 | 37 |
| 2003 | 10 | 36 |
| 2002 | 3.8 | 40 |
| 2001 | 5.7 | 40 |
| 2000 | 7.4 | 39 |
| 1999 | 8.7 | 37 |
| 1998 | 5.3 | 48 |
| 1997 | 8.7 | 40 |
| 1996 | 1.4 | 57 |
| 1995 | 15.1 | 20 |
| 1994 | 9.3 | 31 |
| 1993 | 5.4 | 34 |
| 1992 | 4.2 | 27 |
| 1991 | 4.7 | 25 |
| 1990 | 4.8 | 25 |
| 1989 | 6.3 | 23 |
| 1988 | 5.9 | 19 |
| 1987 | 5.7 | 24 |
| 1986 | 4 | 23 |