| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 77.4 | 4 |
| 2015 | 76.8 | 5 |
| 2014 | 77 | 4 |
| 2013 | 77.2 | 4 |
| 2012 | 77.4 | 4 |
| 2011 | 77.5 | 4 |
| 2010 | 77.6 | 4 |
| 2009 | 76.9 | 4 |
| 2008 | 76 | 4 |
| 2007 | 74.9 | 4 |
| 2006 | 73.6 | 5 |
| 2005 | 72.1 | 8 |
| 2004 | 71.4 | 9 |
| 2003 | 70.5 | 11 |
| 2002 | 69.6 | 14 |
| 2001 | 68.5 | 19 |
| 2000 | 67.4 | 39 |
| 1999 | 67.6 | 35 |
| 1998 | 67.7 | 28 |
| 1997 | 67.6 | 24 |
| 1996 | 67.5 | 27 |
| 1995 | 67.4 | 28 |
| 1994 | 66.8 | 33 |
| 1993 | 66.2 | 43 |
| 1992 | 65.7 | 50 |
| 1991 | 65.3 | 53 |
| 1990 | 65.1 | 54 |
| 1989 | 64.7 | 54 |
| 1988 | 64.4 | 57 |
| 1987 | 64.2 | 58 |
| 1986 | 63.9 | 58 |