| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 24.6 | 104 |
| 2015 | 25 | 104 |
| 2014 | 25.5 | 103 |
| 2013 | 26 | 102 |
| 2012 | 26.6 | 101 |
| 2011 | 27.2 | 100 |
| 2010 | 27.9 | 97 |
| 2009 | 28.5 | 97 |
| 2008 | 29 | 96 |
| 2007 | 29.5 | 95 |
| 2006 | 30 | 97 |
| 2005 | 30.5 | 96 |
| 2004 | 31.1 | 96 |
| 2003 | 31.7 | 95 |
| 2002 | 32.4 | 95 |
| 2001 | 32.9 | 98 |
| 2000 | 33.4 | 99 |
| 1999 | 33.9 | 99 |
| 1998 | 34.4 | 99 |
| 1997 | 34.8 | 99 |
| 1996 | 35.2 | 99 |
| 1995 | 35.6 | 99 |
| 1994 | 35.9 | 100 |
| 1993 | 36.2 | 99 |
| 1992 | 36.5 | 100 |
| 1991 | 36.7 | 101 |
| 1990 | 37 | 102 |
| 1989 | 37.3 | 101 |
| 1988 | 37.6 | 101 |
| 1987 | 37.9 | 103 |
| 1986 | 38.1 | 103 |