| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 18.2 | 145 |
| 2015 | 18.3 | 145 |
| 2014 | 18.3 | 146 |
| 2013 | 18.4 | 146 |
| 2012 | 18.4 | 147 |
| 2011 | 18.4 | 148 |
| 2010 | 18.4 | 148 |
| 2009 | 18.4 | 148 |
| 2008 | 18.4 | 150 |
| 2007 | 18.4 | 155 |
| 2006 | 18.4 | 157 |
| 2005 | 18.4 | 160 |
| 2004 | 18.5 | 161 |
| 2003 | 18.5 | 164 |
| 2002 | 18.6 | 166 |
| 2001 | 18.7 | 168 |
| 2000 | 18.8 | 168 |
| 1999 | 18.9 | 170 |
| 1998 | 19 | 171 |
| 1997 | 19.2 | 172 |
| 1996 | 19.3 | 173 |
| 1995 | 19.5 | 173 |
| 1994 | 19.5 | 171 |
| 1993 | 19.6 | 172 |
| 1992 | 19.6 | 175 |
| 1991 | 19.7 | 177 |
| 1990 | 19.9 | 178 |
| 1989 | 20.1 | 178 |
| 1988 | 20.3 | 178 |
| 1987 | 20.6 | 177 |
| 1986 | 20.9 | 178 |