| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 28 | 86 |
| 2015 | 28.1 | 88 |
| 2014 | 28.1 | 90 |
| 2013 | 28.3 | 92 |
| 2012 | 28.6 | 90 |
| 2011 | 28.9 | 91 |
| 2010 | 29.1 | 91 |
| 2009 | 29.7 | 90 |
| 2008 | 30.3 | 88 |
| 2007 | 31 | 86 |
| 2006 | 31.7 | 85 |
| 2005 | 32.6 | 84 |
| 2004 | 33.5 | 81 |
| 2003 | 34.5 | 82 |
| 2002 | 35.4 | 81 |
| 2001 | 36.3 | 79 |
| 2000 | 37.3 | 77 |
| 1999 | 38 | 77 |
| 1998 | 38.7 | 77 |
| 1997 | 39.3 | 75 |
| 1996 | 39.8 | 75 |
| 1995 | 40.2 | 75 |
| 1994 | 40.5 | 78 |
| 1993 | 40.6 | 77 |
| 1992 | 40.7 | 78 |
| 1991 | 40.7 | 79 |
| 1990 | 40.7 | 79 |
| 1989 | 40.7 | 80 |
| 1988 | 40.6 | 81 |
| 1987 | 40.6 | 83 |
| 1986 | 40.5 | 84 |