| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 22.7 | 118 |
| 2015 | 22.8 | 118 |
| 2014 | 23.1 | 117 |
| 2013 | 23.3 | 117 |
| 2012 | 23.5 | 117 |
| 2011 | 23.8 | 117 |
| 2010 | 24.1 | 116 |
| 2009 | 24.7 | 116 |
| 2008 | 25.4 | 116 |
| 2007 | 26.2 | 116 |
| 2006 | 26.8 | 114 |
| 2005 | 27.5 | 114 |
| 2004 | 27.9 | 116 |
| 2003 | 28.2 | 117 |
| 2002 | 28.5 | 119 |
| 2001 | 28.7 | 120 |
| 2000 | 29 | 121 |
| 1999 | 29.2 | 122 |
| 1998 | 29.4 | 123 |
| 1997 | 29.6 | 122 |
| 1996 | 29.8 | 124 |
| 1995 | 29.9 | 125 |
| 1994 | 30.2 | 125 |
| 1993 | 30.5 | 127 |
| 1992 | 30.8 | 126 |
| 1991 | 31.2 | 125 |
| 1990 | 31.9 | 124 |
| 1989 | 32.5 | 123 |
| 1988 | 33.4 | 119 |
| 1987 | 34.3 | 118 |
| 1986 | 35.1 | 116 |