| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 25.1 | 103 |
| 2015 | 25.2 | 103 |
| 2014 | 25.3 | 104 |
| 2013 | 25.5 | 104 |
| 2012 | 25.6 | 105 |
| 2011 | 25.7 | 108 |
| 2010 | 25.9 | 109 |
| 2009 | 26.1 | 111 |
| 2008 | 26.3 | 111 |
| 2007 | 26.5 | 112 |
| 2006 | 26.7 | 116 |
| 2005 | 26.9 | 118 |
| 2004 | 27.1 | 121 |
| 2003 | 27.3 | 121 |
| 2002 | 27.5 | 124 |
| 2001 | 27.7 | 125 |
| 2000 | 28 | 126 |
| 1999 | 28.2 | 126 |
| 1998 | 28.4 | 126 |
| 1997 | 28.6 | 127 |
| 1996 | 28.9 | 128 |
| 1995 | 29.1 | 129 |
| 1994 | 29.4 | 129 |
| 1993 | 29.8 | 129 |
| 1992 | 30.2 | 129 |
| 1991 | 30.5 | 128 |
| 1990 | 30.6 | 129 |
| 1989 | 30.8 | 128 |
| 1988 | 30.8 | 129 |
| 1987 | 30.8 | 130 |
| 1986 | 30.8 | 133 |