| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 27.1 | 96 |
| 2015 | 27.5 | 95 |
| 2014 | 27.9 | 94 |
| 2013 | 28.4 | 90 |
| 2012 | 28.8 | 87 |
| 2011 | 29.3 | 87 |
| 2010 | 29.8 | 85 |
| 2009 | 30.3 | 84 |
| 2008 | 30.8 | 84 |
| 2007 | 31.3 | 83 |
| 2006 | 31.8 | 84 |
| 2005 | 32.3 | 86 |
| 2004 | 32.7 | 87 |
| 2003 | 33.1 | 87 |
| 2002 | 33.5 | 88 |
| 2001 | 33.9 | 90 |
| 2000 | 34.3 | 94 |
| 1999 | 34.6 | 94 |
| 1998 | 35 | 96 |
| 1997 | 35.4 | 97 |
| 1996 | 35.8 | 97 |
| 1995 | 36.2 | 96 |
| 1994 | 36.7 | 96 |
| 1993 | 37.2 | 95 |
| 1992 | 37.8 | 92 |
| 1991 | 38.4 | 90 |
| 1990 | 39.1 | 88 |
| 1989 | 39.8 | 85 |
| 1988 | 40.5 | 84 |
| 1987 | 41.3 | 78 |
| 1986 | 42.1 | 73 |