| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 17.7 | 148 |
| 2015 | 17.7 | 149 |
| 2014 | 17.7 | 149 |
| 2013 | 17.7 | 149 |
| 2012 | 17.6 | 149 |
| 2011 | 17.7 | 151 |
| 2010 | 17.8 | 152 |
| 2009 | 18.1 | 153 |
| 2008 | 18.4 | 151 |
| 2007 | 18.8 | 150 |
| 2006 | 19.3 | 150 |
| 2005 | 19.9 | 149 |
| 2004 | 20.7 | 145 |
| 2003 | 21.8 | 143 |
| 2002 | 22.9 | 139 |
| 2001 | 23.9 | 139 |
| 2000 | 24.6 | 138 |
| 1999 | 25.4 | 137 |
| 1998 | 25.9 | 137 |
| 1997 | 26.3 | 137 |
| 1996 | 26.7 | 137 |
| 1995 | 27.4 | 134 |
| 1994 | 27.7 | 135 |
| 1993 | 28.1 | 134 |
| 1992 | 28.5 | 134 |
| 1991 | 28.7 | 134 |
| 1990 | 28.8 | 136 |
| 1989 | 29.1 | 135 |
| 1988 | 29.4 | 135 |
| 1987 | 29.7 | 135 |
| 1986 | 30.1 | 135 |