| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 6.7 | 32 |
| 2015 | 9.5 | 26 |
| 2014 | 8.6 | 38 |
| 2013 | 10.2 | 35 |
| 2012 | 8.8 | 35 |
| 2011 | 13.5 | 32 |
| 2010 | 32.5 | 25 |
| 2009 | 54.2 | 16 |
| 2008 | 123.8 | 5 |
| 2007 | 101.8 | 15 |
| 2006 | 129.9 | 5 |
| 2005 | 189.2 | 4 |
| 2004 | 46.9 | 21 |
| 2003 | 25.7 | 24 |
| 2002 | 14 | 28 |
| 2001 | 10.5 | 35 |
| 2000 | 5.6 | 43 |
| 1999 | 6.7 | 39 |
| 1998 | 8.2 | 42 |
| 1997 | 6.9 | 44 |
| 1996 | 5.1 | 39 |
| 1995 | 8.8 | 32 |
| 1994 | 11.3 | 27 |
| 1993 | 23.7 | 10 |