| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 26.9 | 97 |
| 2015 | 27.4 | 96 |
| 2014 | 28 | 93 |
| 2013 | 28.6 | 86 |
| 2012 | 29.3 | 83 |
| 2011 | 29.9 | 83 |
| 2010 | 30.6 | 81 |
| 2009 | 31.4 | 79 |
| 2008 | 32.2 | 78 |
| 2007 | 33 | 77 |
| 2006 | 34 | 77 |
| 2005 | 34.9 | 75 |
| 2004 | 36.1 | 73 |
| 2003 | 37.4 | 70 |
| 2002 | 38.8 | 67 |
| 2001 | 40.1 | 63 |
| 2000 | 41.4 | 53 |
| 1999 | 42.2 | 50 |
| 1998 | 42.9 | 49 |
| 1997 | 43.4 | 48 |
| 1996 | 44 | 45 |
| 1995 | 44.5 | 36 |
| 1994 | 44.4 | 44 |
| 1993 | 44.3 | 49 |
| 1992 | 44.2 | 52 |
| 1991 | 44.1 | 54 |
| 1990 | 43.9 | 56 |
| 1989 | 44.1 | 54 |
| 1988 | 44.2 | 56 |
| 1987 | 44.2 | 58 |
| 1986 | 44.1 | 59 |