| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 27.7 | 91 |
| 2015 | 27.9 | 93 |
| 2014 | 28.1 | 92 |
| 2013 | 28.3 | 91 |
| 2012 | 28.5 | 91 |
| 2011 | 28.7 | 93 |
| 2010 | 29 | 93 |
| 2009 | 29.1 | 94 |
| 2008 | 29.2 | 95 |
| 2007 | 29.5 | 96 |
| 2006 | 29.7 | 98 |
| 2005 | 30 | 100 |
| 2004 | 30.1 | 101 |
| 2003 | 30.2 | 103 |
| 2002 | 30.3 | 106 |
| 2001 | 30.5 | 109 |
| 2000 | 30.7 | 111 |
| 1999 | 31.2 | 112 |
| 1998 | 31.8 | 112 |
| 1997 | 32.5 | 111 |
| 1996 | 33.1 | 111 |
| 1995 | 33.7 | 108 |
| 1994 | 34.3 | 107 |
| 1993 | 34.8 | 107 |
| 1992 | 35.3 | 107 |
| 1991 | 35.9 | 106 |
| 1990 | 36.4 | 104 |
| 1989 | 37 | 103 |
| 1988 | 37.6 | 102 |
| 1987 | 38.1 | 101 |
| 1986 | 38.6 | 100 |