| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 68.3 | 47 |
| 2015 | 67.9 | 49 |
| 2014 | 67.5 | 58 |
| 2013 | 66.9 | 69 |
| 2012 | 66.4 | 83 |
| 2011 | 65.8 | 90 |
| 2010 | 65.3 | 99 |
| 2009 | 64.5 | 106 |
| 2008 | 63.8 | 108 |
| 2007 | 63 | 111 |
| 2006 | 62.2 | 115 |
| 2005 | 61.3 | 119 |
| 2004 | 60.1 | 120 |
| 2003 | 58.9 | 122 |
| 2002 | 57.6 | 127 |
| 2001 | 56.3 | 131 |
| 2000 | 55.1 | 142 |
| 1999 | 54.4 | 142 |
| 1998 | 53.8 | 144 |
| 1997 | 53.3 | 147 |
| 1996 | 52.8 | 150 |
| 1995 | 52.4 | 154 |
| 1994 | 52.6 | 150 |
| 1993 | 52.7 | 143 |
| 1992 | 52.8 | 138 |
| 1991 | 53 | 130 |
| 1990 | 53.4 | 126 |
| 1989 | 53.1 | 128 |
| 1988 | 53.1 | 128 |
| 1987 | 53.1 | 130 |
| 1986 | 53.2 | 130 |