| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 27 | 26 |
| 2015 | 29.1 | 26 |
| 2014 | 31.1 | 28 |
| 2013 | 28.4 | 29 |
| 2012 | 26.5 | 29 |
| 2011 | 32.9 | 31 |
| 2010 | 28.1 | 35 |
| 2009 | 28 | 37 |
| 2008 | 43.5 | 37 |
| 2007 | 47.5 | 26 |
| 2006 | 29.4 | 31 |
| 2005 | 24.7 | 32 |
| 2004 | 29.8 | 30 |
| 2003 | 28.4 | 29 |
| 2002 | 20.5 | 32 |
| 2001 | 17.7 | 41 |
| 2000 | 46.4 | 27 |
| 1999 | 30.1 | 32 |
| 1998 | 27.8 | 38 |
| 1997 | 45.7 | 27 |
| 1996 | 8.4 | 39 |
| 1995 | 28.1 | 25 |
| 1994 | 6.5 | 38 |
| 1993 | 6.6 | 33 |
| 1992 | 20.9 | 20 |
| 1991 | 18.8 | 21 |
| 1990 | 22.4 | 18 |
| 1989 | 16.6 | 20 |
| 1988 | 10.9 | 23 |
| 1987 | 20.9 | 19 |
| 1986 | 7.9 | 24 |