| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 29 | 80 |
| 2015 | 28.7 | 84 |
| 2014 | 28.3 | 88 |
| 2013 | 28 | 93 |
| 2012 | 27.7 | 96 |
| 2011 | 27.4 | 98 |
| 2010 | 27.2 | 101 |
| 2009 | 27.3 | 102 |
| 2008 | 27.5 | 103 |
| 2007 | 27.9 | 104 |
| 2006 | 28.4 | 104 |
| 2005 | 29.1 | 103 |
| 2004 | 29.9 | 102 |
| 2003 | 30.9 | 102 |
| 2002 | 31.9 | 98 |
| 2001 | 33.1 | 96 |
| 2000 | 34.3 | 93 |
| 1999 | 35.4 | 89 |
| 1998 | 36.6 | 84 |
| 1997 | 37.7 | 83 |
| 1996 | 38.8 | 83 |
| 1995 | 39.7 | 79 |
| 1994 | 40.6 | 74 |
| 1993 | 41.4 | 71 |
| 1992 | 42.1 | 70 |
| 1991 | 42.8 | 68 |
| 1990 | 43.3 | 64 |
| 1989 | 43.9 | 58 |
| 1988 | 44.4 | 53 |
| 1987 | 44.8 | 51 |
| 1986 | 45.1 | 46 |