| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 29.7 | 74 |
| 2015 | 30.1 | 74 |
| 2014 | 30.6 | 73 |
| 2013 | 31.1 | 72 |
| 2012 | 31.7 | 72 |
| 2011 | 32.2 | 72 |
| 2010 | 32.7 | 73 |
| 2009 | 33.2 | 74 |
| 2008 | 33.7 | 74 |
| 2007 | 34.2 | 73 |
| 2006 | 34.7 | 73 |
| 2005 | 35.3 | 73 |
| 2004 | 35.9 | 74 |
| 2003 | 36.5 | 73 |
| 2002 | 37.1 | 73 |
| 2001 | 37.7 | 74 |
| 2000 | 38.2 | 74 |
| 1999 | 38.7 | 72 |
| 1998 | 39.2 | 72 |
| 1997 | 39.6 | 73 |
| 1996 | 39.9 | 74 |
| 1995 | 40.2 | 74 |
| 1994 | 40.5 | 75 |
| 1993 | 40.8 | 76 |
| 1992 | 41 | 74 |
| 1991 | 41.1 | 74 |
| 1990 | 41.3 | 76 |
| 1989 | 41.3 | 75 |
| 1988 | 41.4 | 74 |
| 1987 | 41.4 | 77 |
| 1986 | 41.5 | 79 |