| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 11.3 | 38 |
| 2015 | 10.3 | 37 |
| 2014 | 11.6 | 42 |
| 2013 | 15.5 | 37 |
| 2012 | 14.8 | 37 |
| 2011 | 19 | 39 |
| 2010 | 16.9 | 42 |
| 2009 | 16.1 | 45 |
| 2008 | 21.9 | 48 |
| 2007 | 21.2 | 44 |
| 2006 | 15.9 | 42 |
| 2005 | 15 | 42 |
| 2004 | 11.2 | 48 |
| 2003 | 8.7 | 46 |
| 2002 | 5.3 | 47 |
| 2001 | 7.2 | 51 |
| 2000 | 9.5 | 47 |
| 1999 | 9.6 | 45 |
| 1998 | 8.3 | 48 |
| 1997 | 10.3 | 44 |
| 1996 | 1.6 | 56 |
| 1995 | 15.2 | 32 |
| 1994 | 7.8 | 37 |
| 1993 | 5.9 | 34 |
| 1992 | 6 | 26 |
| 1991 | 6.3 | 26 |