| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 5.9 | 35 |
| 2015 | 5.2 | 35 |
| 2014 | 4.3 | 47 |
| 2013 | 4.6 | 46 |
| 2012 | 3 | 48 |
| 2010 | 1.3 | 61 |
| 2009 | 2.7 | 54 |
| 2008 | 2.5 | 58 |
| 2007 | 4.3 | 58 |
| 2006 | 4.8 | 54 |
| 2005 | 4.8 | 45 |
| 2004 | 4.9 | 47 |
| 2003 | 4.4 | 42 |
| 2002 | 3.9 | 39 |
| 2001 | 15.8 | 30 |
| 2000 | 19 | 29 |
| 1999 | 20.5 | 30 |
| 1998 | 20.9 | 27 |
| 1997 | 13.4 | 32 |
| 1996 | 13.8 | 25 |
| 1995 | 13.1 | 24 |
| 1994 | 13.4 | 23 |
| 1993 | 14.4 | 18 |
| 1992 | 7.3 | 20 |
| 1991 | 6.3 | 23 |
| 1990 | 4.2 | 26 |
| 1989 | 2.1 | 28 |
| 1988 | 2.4 | 29 |
| 1987 | 7.3 | 23 |
| 1986 | 7 | 16 |