| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 26.4 | 99 |
| 2015 | 26.5 | 99 |
| 2014 | 26.6 | 98 |
| 2013 | 26.8 | 99 |
| 2012 | 27 | 99 |
| 2011 | 27.3 | 99 |
| 2010 | 27.5 | 98 |
| 2009 | 27.9 | 99 |
| 2008 | 28.2 | 100 |
| 2007 | 28.6 | 102 |
| 2006 | 29.2 | 101 |
| 2005 | 30 | 101 |
| 2004 | 30.9 | 97 |
| 2003 | 32 | 93 |
| 2002 | 33.2 | 91 |
| 2001 | 34.2 | 88 |
| 2000 | 35 | 85 |
| 1999 | 35.8 | 85 |
| 1998 | 36.5 | 86 |
| 1997 | 36.9 | 86 |
| 1996 | 37.4 | 86 |
| 1995 | 38.1 | 85 |
| 1994 | 38.6 | 85 |
| 1993 | 38.9 | 86 |
| 1992 | 39.1 | 86 |
| 1991 | 39.1 | 87 |
| 1990 | 38.9 | 89 |
| 1989 | 38.7 | 91 |
| 1988 | 38.5 | 94 |
| 1987 | 38.5 | 97 |
| 1986 | 38.3 | 102 |