| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 25.1 | 102 |
| 2015 | 25.4 | 102 |
| 2014 | 25.8 | 102 |
| 2013 | 26.2 | 100 |
| 2012 | 26.6 | 100 |
| 2011 | 27 | 102 |
| 2010 | 27.5 | 99 |
| 2009 | 27.9 | 98 |
| 2008 | 28.4 | 98 |
| 2007 | 28.8 | 100 |
| 2006 | 29.2 | 102 |
| 2005 | 29.5 | 102 |
| 2004 | 29.8 | 104 |
| 2003 | 30 | 104 |
| 2002 | 30.2 | 108 |
| 2001 | 30.4 | 110 |
| 2000 | 30.5 | 114 |
| 1999 | 30.7 | 115 |
| 1998 | 30.9 | 117 |
| 1997 | 31 | 117 |
| 1996 | 31 | 118 |
| 1995 | 30.9 | 120 |
| 1994 | 30.8 | 123 |
| 1993 | 30.5 | 126 |
| 1992 | 30.3 | 128 |
| 1991 | 30 | 130 |
| 1990 | 29.9 | 133 |
| 1989 | 30.2 | 130 |
| 1988 | 30.7 | 130 |
| 1987 | 31.1 | 129 |
| 1986 | 31.6 | 129 |