| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 29.5 | 76 |
| 2015 | 30 | 75 |
| 2014 | 30.5 | 74 |
| 2013 | 31.1 | 73 |
| 2012 | 31.6 | 73 |
| 2011 | 32.2 | 73 |
| 2010 | 32.8 | 72 |
| 2009 | 33.4 | 71 |
| 2008 | 34 | 72 |
| 2007 | 34.6 | 72 |
| 2006 | 35.2 | 72 |
| 2005 | 36 | 72 |
| 2004 | 36.6 | 71 |
| 2003 | 37.4 | 71 |
| 2002 | 38.1 | 69 |
| 2001 | 38.9 | 69 |
| 2000 | 39.6 | 69 |
| 1999 | 40.4 | 68 |
| 1998 | 41.1 | 66 |
| 1997 | 41.8 | 62 |
| 1996 | 42.5 | 57 |
| 1995 | 43.2 | 52 |
| 1994 | 43.8 | 51 |
| 1993 | 44.3 | 47 |
| 1992 | 44.8 | 41 |
| 1991 | 45.3 | 36 |
| 1990 | 45.7 | 34 |
| 1989 | 46.1 | 28 |
| 1988 | 46.4 | 23 |
| 1987 | 46.6 | 21 |
| 1986 | 46.8 | 18 |