| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 27.9 | 87 |
| 2015 | 27.9 | 92 |
| 2014 | 27.8 | 96 |
| 2013 | 27.7 | 96 |
| 2012 | 27.6 | 97 |
| 2011 | 27.4 | 97 |
| 2010 | 27.3 | 100 |
| 2009 | 27.4 | 101 |
| 2008 | 27.5 | 104 |
| 2007 | 27.6 | 108 |
| 2006 | 27.7 | 109 |
| 2005 | 27.9 | 110 |
| 2004 | 27.9 | 117 |
| 2003 | 27.9 | 120 |
| 2002 | 28 | 121 |
| 2001 | 28.1 | 123 |
| 2000 | 28.1 | 125 |
| 1999 | 28.2 | 125 |
| 1998 | 28.4 | 127 |
| 1997 | 28.5 | 128 |
| 1996 | 28.7 | 129 |
| 1995 | 29 | 130 |
| 1994 | 29.4 | 130 |
| 1993 | 29.9 | 128 |
| 1992 | 30.4 | 127 |
| 1991 | 30.8 | 127 |
| 1990 | 31.3 | 127 |
| 1989 | 31.6 | 125 |
| 1988 | 32 | 124 |
| 1987 | 32.3 | 126 |
| 1986 | 32.6 | 125 |