| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 27.6 | 92 |
| 2015 | 27.9 | 91 |
| 2014 | 28.1 | 91 |
| 2013 | 28.4 | 89 |
| 2012 | 28.7 | 89 |
| 2011 | 28.9 | 90 |
| 2010 | 29.1 | 90 |
| 2009 | 29.4 | 91 |
| 2008 | 29.7 | 92 |
| 2007 | 29.9 | 93 |
| 2006 | 30.1 | 95 |
| 2005 | 30.4 | 97 |
| 2004 | 30.7 | 98 |
| 2003 | 31.1 | 100 |
| 2002 | 31.4 | 103 |
| 2001 | 31.7 | 103 |
| 2000 | 32 | 104 |
| 1999 | 32.3 | 106 |
| 1998 | 32.6 | 107 |
| 1997 | 32.9 | 109 |
| 1996 | 33.3 | 108 |
| 1995 | 33.6 | 109 |
| 1994 | 34 | 109 |
| 1993 | 34.5 | 108 |
| 1992 | 35 | 108 |
| 1991 | 35.4 | 108 |
| 1990 | 35.9 | 107 |
| 1989 | 36.4 | 106 |
| 1988 | 36.9 | 106 |
| 1987 | 37.4 | 104 |
| 1986 | 37.9 | 104 |