| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 0.4 | 50 |
| 2015 | 0.7 | 51 |
| 2014 | 0.2 | 66 |
| 2013 | 0.2 | 75 |
| 2012 | 1.2 | 57 |
| 2011 | 1.6 | 59 |
| 2010 | 2.9 | 54 |
| 2009 | 6.8 | 46 |
| 2008 | 6.4 | 49 |
| 2007 | 18.5 | 40 |
| 2006 | 15.4 | 39 |
| 2005 | 2.5 | 55 |
| 2004 | 1.5 | 66 |
| 2003 | 2.1 | 52 |
| 2002 | 5.7 | 37 |
| 2001 | 29.8 | 21 |
| 2000 | 93.7 | 11 |
| 1999 | 60.4 | 12 |
| 1998 | 6.8 | 45 |
| 1997 | 4.2 | 50 |
| 1996 | 4.6 | 41 |
| 1995 | 3 | 44 |
| 1994 | 1.2 | 53 |
| 1993 | 0.4 | 51 |