| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 71.4 | 14 |
| 2015 | 71.4 | 14 |
| 2014 | 71.6 | 14 |
| 2013 | 71.7 | 14 |
| 2012 | 71.7 | 13 |
| 2011 | 71.8 | 13 |
| 2010 | 71.9 | 13 |
| 2009 | 71.8 | 13 |
| 2008 | 71.6 | 13 |
| 2007 | 71.4 | 13 |
| 2006 | 71.2 | 13 |
| 2005 | 70.9 | 14 |
| 2004 | 70.7 | 13 |
| 2003 | 70.4 | 13 |
| 2002 | 70.1 | 10 |
| 2001 | 69.8 | 10 |
| 2000 | 69.5 | 10 |
| 1999 | 69.1 | 10 |
| 1998 | 68.8 | 11 |
| 1997 | 68.3 | 14 |
| 1996 | 67.9 | 19 |
| 1995 | 67.4 | 25 |
| 1994 | 67.1 | 29 |
| 1993 | 66.7 | 32 |
| 1992 | 66.2 | 39 |
| 1991 | 65.8 | 47 |
| 1990 | 65.3 | 51 |
| 1989 | 64.6 | 56 |
| 1988 | 63.8 | 61 |
| 1987 | 63 | 63 |
| 1986 | 62.1 | 66 |