| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 3.1 | 39 |
| 2015 | 2.9 | 40 |
| 2014 | 2.8 | 51 |
| 2013 | 3 | 49 |
| 2012 | 3.6 | 46 |
| 2011 | 4 | 47 |
| 2010 | 6.5 | 45 |
| 2009 | 8.5 | 43 |
| 2008 | 14.9 | 37 |
| 2007 | 29.3 | 35 |
| 2006 | 14.4 | 40 |
| 2005 | 12.7 | 38 |
| 2004 | 6.6 | 44 |
| 2003 | 5 | 40 |
| 2002 | 2.4 | 47 |
| 2001 | 4.4 | 44 |
| 2000 | 8.1 | 37 |
| 1999 | 20.1 | 31 |
| 1998 | 12.5 | 36 |
| 1997 | 8.1 | 42 |
| 1996 | 4.8 | 40 |
| 1995 | 6.3 | 36 |
| 1994 | 2.3 | 48 |
| 1993 | 1.5 | 44 |