| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 72.5 | 11 |
| 2015 | 72.5 | 12 |
| 2014 | 72.2 | 12 |
| 2013 | 71.9 | 12 |
| 2012 | 71.4 | 17 |
| 2011 | 70.8 | 20 |
| 2010 | 70.1 | 29 |
| 2009 | 69.2 | 36 |
| 2008 | 68.1 | 48 |
| 2007 | 66.9 | 66 |
| 2006 | 65.5 | 85 |
| 2005 | 64.2 | 96 |
| 2004 | 62.6 | 103 |
| 2003 | 60.9 | 113 |
| 2002 | 59.2 | 119 |
| 2001 | 57.4 | 124 |
| 2000 | 55.6 | 135 |
| 1999 | 54.4 | 143 |
| 1998 | 53.2 | 151 |
| 1997 | 52.2 | 160 |
| 1996 | 51.3 | 170 |
| 1995 | 50.5 | 178 |
| 1994 | 50 | 180 |
| 1993 | 49.7 | 181 |
| 1992 | 49.6 | 182 |
| 1991 | 49.6 | 181 |
| 1990 | 49.7 | 179 |
| 1989 | 49.8 | 179 |
| 1988 | 50 | 177 |
| 1987 | 50.2 | 175 |
| 1986 | 50.5 | 165 |