| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 74 | 7 |
| 2015 | 74.3 | 7 |
| 2014 | 74.3 | 7 |
| 2013 | 74.2 | 8 |
| 2012 | 73.9 | 7 |
| 2011 | 73.6 | 9 |
| 2010 | 73.3 | 9 |
| 2009 | 73.1 | 9 |
| 2008 | 72.8 | 10 |
| 2007 | 72.5 | 10 |
| 2006 | 72 | 10 |
| 2005 | 71.6 | 10 |
| 2004 | 70.7 | 12 |
| 2003 | 69.8 | 16 |
| 2002 | 68.8 | 20 |
| 2001 | 67.9 | 33 |
| 2000 | 67.1 | 44 |
| 1999 | 66.4 | 52 |
| 1998 | 65.8 | 54 |
| 1997 | 65.3 | 57 |
| 1996 | 64.8 | 58 |
| 1995 | 64.4 | 63 |
| 1994 | 64 | 66 |
| 1993 | 63.8 | 66 |
| 1992 | 63.6 | 66 |
| 1991 | 63.6 | 67 |
| 1990 | 63.8 | 63 |
| 1989 | 64 | 62 |
| 1988 | 64.2 | 58 |
| 1987 | 64.5 | 54 |
| 1986 | 64.9 | 49 |