| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 18.3 | 142 |
| 2015 | 18.7 | 143 |
| 2014 | 19 | 140 |
| 2013 | 19.5 | 141 |
| 2012 | 19.9 | 138 |
| 2011 | 20.3 | 139 |
| 2010 | 20.6 | 137 |
| 2009 | 21 | 135 |
| 2008 | 21.4 | 133 |
| 2007 | 21.7 | 133 |
| 2006 | 22 | 134 |
| 2005 | 22.3 | 134 |
| 2004 | 22.6 | 134 |
| 2003 | 22.8 | 136 |
| 2002 | 23 | 138 |
| 2001 | 23.3 | 141 |
| 2000 | 23.6 | 141 |
| 1999 | 23.9 | 142 |
| 1998 | 24.3 | 142 |
| 1997 | 24.7 | 143 |
| 1996 | 25 | 142 |
| 1995 | 25.3 | 142 |
| 1994 | 25.7 | 142 |
| 1993 | 26 | 141 |
| 1992 | 26.4 | 141 |
| 1991 | 26.8 | 141 |
| 1990 | 27.2 | 141 |
| 1989 | 27.6 | 139 |
| 1988 | 28.1 | 139 |
| 1987 | 28.6 | 139 |
| 1986 | 29.1 | 140 |