| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 14.5 | 33 |
| 2015 | 16.1 | 33 |
| 2014 | 16.1 | 38 |
| 2013 | 20.5 | 35 |
| 2012 | 15.6 | 36 |
| 2011 | 16.6 | 40 |
| 2010 | 14.1 | 46 |
| 2009 | 16.6 | 43 |
| 2008 | 23.8 | 45 |
| 2007 | 23.6 | 42 |
| 2006 | 13.5 | 43 |
| 2005 | 13.5 | 43 |
| 2004 | 11.3 | 46 |
| 2003 | 10.5 | 42 |
| 2002 | 11.6 | 39 |
| 2001 | 14.2 | 42 |
| 2000 | 28.4 | 35 |
| 1999 | 45.9 | 21 |
| 1998 | 29.8 | 37 |
| 1997 | 64.9 | 14 |
| 1996 | 31.6 | 25 |