| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 16.2 | 163 |
| 2015 | 16.3 | 161 |
| 2014 | 16.5 | 159 |
| 2013 | 16.6 | 159 |
| 2012 | 16.9 | 158 |
| 2011 | 17.1 | 158 |
| 2010 | 17.4 | 157 |
| 2009 | 17.7 | 156 |
| 2008 | 18.1 | 155 |
| 2007 | 18.4 | 154 |
| 2006 | 18.9 | 152 |
| 2005 | 19.4 | 153 |
| 2004 | 19.9 | 152 |
| 2003 | 20.4 | 151 |
| 2002 | 21 | 151 |
| 2001 | 21.5 | 152 |
| 2000 | 21.8 | 151 |
| 1999 | 22.1 | 151 |
| 1998 | 22.2 | 153 |
| 1997 | 22.3 | 155 |
| 1996 | 22.3 | 156 |
| 1995 | 22.6 | 156 |
| 1994 | 22.6 | 156 |
| 1993 | 22.6 | 158 |
| 1992 | 22.7 | 160 |
| 1991 | 22.9 | 160 |
| 1990 | 23.2 | 160 |
| 1989 | 23.6 | 157 |
| 1988 | 24.3 | 156 |
| 1987 | 25 | 152 |
| 1986 | 25.8 | 148 |