| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 56.5 | 158 |
| 2015 | 56.1 | 159 |
| 2014 | 55.7 | 159 |
| 2013 | 55.3 | 160 |
| 2012 | 54.9 | 161 |
| 2011 | 54.5 | 164 |
| 2010 | 54.3 | 164 |
| 2009 | 54.1 | 164 |
| 2008 | 54 | 162 |
| 2007 | 53.9 | 162 |
| 2006 | 53.8 | 163 |
| 2005 | 53.6 | 165 |
| 2004 | 53.3 | 163 |
| 2003 | 53 | 166 |
| 2002 | 52.7 | 167 |
| 2001 | 52.4 | 167 |
| 2000 | 52.2 | 166 |
| 1999 | 51.8 | 169 |
| 1998 | 51.5 | 169 |
| 1997 | 51.3 | 172 |
| 1996 | 51 | 174 |
| 1995 | 50.6 | 176 |
| 1994 | 50.1 | 179 |
| 1993 | 49.6 | 183 |
| 1992 | 49.1 | 189 |
| 1991 | 48.6 | 192 |
| 1990 | 48.3 | 192 |
| 1989 | 47.9 | 189 |
| 1988 | 47.6 | 190 |
| 1987 | 47.4 | 191 |
| 1986 | 47.3 | 191 |