| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 29.4 | 77 |
| 2015 | 29.8 | 77 |
| 2014 | 30.3 | 75 |
| 2013 | 30.8 | 74 |
| 2012 | 31.4 | 74 |
| 2011 | 32 | 75 |
| 2010 | 32.7 | 74 |
| 2009 | 33.3 | 73 |
| 2008 | 34 | 71 |
| 2007 | 34.8 | 71 |
| 2006 | 35.5 | 71 |
| 2005 | 36.2 | 71 |
| 2004 | 36.4 | 72 |
| 2003 | 36.4 | 74 |
| 2002 | 36.3 | 77 |
| 2001 | 36.2 | 81 |
| 2000 | 36.2 | 83 |
| 1999 | 35.9 | 84 |
| 1998 | 35.8 | 89 |
| 1997 | 35.8 | 93 |
| 1996 | 36 | 94 |
| 1995 | 36.1 | 98 |
| 1994 | 36 | 99 |
| 1993 | 35.9 | 101 |
| 1992 | 35.8 | 103 |
| 1991 | 35.9 | 105 |
| 1990 | 36.2 | 106 |
| 1989 | 36.6 | 105 |
| 1988 | 37.2 | 103 |
| 1987 | 38 | 102 |
| 1986 | 38.7 | 98 |