| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 17.7 | 149 |
| 2015 | 18 | 147 |
| 2014 | 18.3 | 147 |
| 2013 | 18.5 | 145 |
| 2012 | 18.8 | 145 |
| 2011 | 19 | 146 |
| 2010 | 19.2 | 145 |
| 2009 | 19.6 | 144 |
| 2008 | 20 | 143 |
| 2007 | 20.4 | 142 |
| 2006 | 20.8 | 141 |
| 2005 | 21.3 | 141 |
| 2004 | 21.8 | 141 |
| 2003 | 22.3 | 140 |
| 2002 | 22.8 | 140 |
| 2001 | 23.4 | 140 |
| 2000 | 24 | 140 |
| 1999 | 24.6 | 140 |
| 1998 | 25.2 | 139 |
| 1997 | 25.8 | 139 |
| 1996 | 26.4 | 138 |
| 1995 | 27.1 | 137 |
| 1994 | 27.7 | 136 |
| 1993 | 28.3 | 133 |
| 1992 | 28.9 | 133 |
| 1991 | 29.5 | 133 |
| 1990 | 30.2 | 130 |
| 1989 | 31.1 | 127 |
| 1988 | 32 | 125 |
| 1987 | 32.9 | 123 |
| 1986 | 33.8 | 120 |