| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 28.2 | 25 |
| 2015 | 25.8 | 28 |
| 2014 | 26.7 | 32 |
| 2013 | 31.1 | 24 |
| 2012 | 22.8 | 31 |
| 2011 | 24.4 | 37 |
| 2010 | 24.5 | 38 |
| 2009 | 22 | 40 |
| 2008 | 36.3 | 40 |
| 2007 | 29.6 | 39 |
| 2006 | 23.5 | 38 |
| 2005 | 22.8 | 34 |
| 2004 | 25.8 | 34 |
| 2003 | 18.8 | 37 |
| 2002 | 24.5 | 30 |
| 2001 | 42 | 27 |
| 2000 | 35.7 | 31 |
| 1999 | 22.7 | 38 |
| 1998 | 30.5 | 36 |
| 1997 | 33 | 30 |
| 1996 | 40.4 | 18 |
| 1995 | 37.7 | 20 |
| 1994 | 43.9 | 17 |
| 1993 | 31.2 | 19 |
| 1992 | 31.8 | 15 |
| 1991 | 30.8 | 15 |
| 1990 | 45.2 | 11 |
| 1989 | 50 | 9 |
| 1988 | 50.5 | 7 |
| 1987 | 115.1 | 3 |
| 1986 | 72.6 | 4 |