| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 24.2 | 106 |
| 2015 | 24.6 | 106 |
| 2014 | 24.9 | 105 |
| 2013 | 25.4 | 105 |
| 2012 | 25.8 | 103 |
| 2011 | 26.2 | 105 |
| 2010 | 26.6 | 105 |
| 2009 | 27 | 104 |
| 2008 | 27.4 | 106 |
| 2007 | 27.8 | 106 |
| 2006 | 28.1 | 107 |
| 2005 | 28.4 | 108 |
| 2004 | 28.6 | 109 |
| 2003 | 28.8 | 113 |
| 2002 | 29.1 | 116 |
| 2001 | 29.3 | 117 |
| 2000 | 29.5 | 119 |
| 1999 | 29.5 | 120 |
| 1998 | 29.4 | 122 |
| 1997 | 29.5 | 124 |
| 1996 | 29.8 | 125 |
| 1995 | 30.3 | 123 |
| 1994 | 30.5 | 124 |
| 1993 | 30.7 | 123 |
| 1992 | 30.8 | 125 |
| 1991 | 30.9 | 126 |
| 1990 | 31.3 | 126 |
| 1989 | 30.6 | 129 |
| 1988 | 30.4 | 132 |
| 1987 | 30.5 | 133 |
| 1986 | 30.9 | 131 |