| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 76.8 | 5 |
| 2015 | 77 | 4 |
| 2014 | 76.7 | 5 |
| 2013 | 76.2 | 5 |
| 2012 | 75.7 | 5 |
| 2011 | 75.2 | 5 |
| 2010 | 74.8 | 6 |
| 2009 | 74.3 | 6 |
| 2008 | 73.8 | 6 |
| 2007 | 73.4 | 6 |
| 2006 | 72.7 | 7 |
| 2005 | 71.9 | 9 |
| 2004 | 71.7 | 8 |
| 2003 | 71.3 | 7 |
| 2002 | 70.8 | 7 |
| 2001 | 70.3 | 7 |
| 2000 | 70 | 7 |
| 1999 | 69.7 | 7 |
| 1998 | 69.4 | 7 |
| 1997 | 69 | 9 |
| 1996 | 68.5 | 10 |
| 1995 | 67.9 | 19 |
| 1994 | 67.5 | 23 |
| 1993 | 66.8 | 28 |
| 1992 | 65.9 | 45 |
| 1991 | 64.9 | 57 |
| 1990 | 63.8 | 64 |
| 1989 | 63 | 64 |
| 1988 | 62.2 | 70 |
| 1987 | 61.6 | 70 |
| 1986 | 61.2 | 69 |