| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2014 | 5.2 | 44 |
| 2013 | 5.9 | 43 |
| 2012 | 8.5 | 38 |
| 2011 | 9 | 37 |
| 2010 | 10.7 | 39 |
| 2009 | 12.9 | 38 |
| 2008 | 13.7 | 40 |
| 2007 | 20 | 39 |
| 2006 | 18.5 | 36 |
| 2005 | 25.3 | 26 |
| 2004 | 15.1 | 35 |
| 2003 | 8.8 | 37 |
| 2002 | 7.2 | 34 |
| 2001 | 5.1 | 42 |
| 2000 | 10.8 | 35 |
| 1999 | 6.1 | 42 |
| 1998 | 7.1 | 44 |
| 1997 | 9.3 | 39 |
| 1996 | 9.5 | 29 |
| 1995 | 4.6 | 39 |
| 1994 | 3.2 | 42 |
| 1993 | 0.6 | 50 |