| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 21 | 125 |
| 2015 | 20.9 | 126 |
| 2014 | 21.3 | 126 |
| 2013 | 21.8 | 124 |
| 2012 | 22.3 | 122 |
| 2011 | 22.8 | 122 |
| 2010 | 23.2 | 122 |
| 2009 | 23.7 | 121 |
| 2008 | 24.1 | 121 |
| 2007 | 24.5 | 123 |
| 2006 | 25.2 | 124 |
| 2005 | 26 | 122 |
| 2004 | 26.3 | 124 |
| 2003 | 26.8 | 125 |
| 2002 | 27.4 | 125 |
| 2001 | 28 | 124 |
| 2000 | 28.4 | 124 |
| 1999 | 28.8 | 124 |
| 1998 | 29.2 | 124 |
| 1997 | 29.6 | 123 |
| 1996 | 30.1 | 121 |
| 1995 | 30.7 | 122 |
| 1994 | 31 | 121 |
| 1993 | 31.7 | 121 |
| 1992 | 32.6 | 119 |
| 1991 | 33.7 | 116 |
| 1990 | 34.9 | 113 |
| 1989 | 35.7 | 110 |
| 1988 | 36.4 | 108 |
| 1987 | 37 | 107 |
| 1986 | 37.5 | 107 |