| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 10.7 | 26 |
| 2015 | 9 | 28 |
| 2014 | 9.9 | 36 |
| 2013 | 13 | 31 |
| 2012 | 10.1 | 33 |
| 2011 | 8.5 | 38 |
| 2010 | 10.6 | 40 |
| 2009 | 8.7 | 42 |
| 2008 | 7.7 | 45 |
| 2007 | 11.3 | 46 |
| 2006 | 8.5 | 46 |
| 2005 | 6.3 | 43 |
| 2004 | 5.7 | 46 |
| 2003 | 3.2 | 46 |
| 2002 | 3.4 | 41 |
| 2001 | 7.3 | 37 |
| 2000 | 6.5 | 40 |
| 1999 | 6 | 43 |
| 1998 | 5.6 | 47 |
| 1997 | 10.8 | 37 |
| 1996 | 10.9 | 28 |
| 1995 | 9.9 | 30 |
| 1994 | 10.8 | 29 |
| 1993 | 12.4 | 21 |
| 1992 | 12.1 | 15 |
| 1991 | 10.1 | 16 |
| 1990 | 7.1 | 22 |
| 1989 | 6.1 | 24 |
| 1988 | 4.2 | 24 |
| 1987 | 7.4 | 21 |
| 1986 | 3.1 | 25 |