| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 29.3 | 78 |
| 2015 | 28.8 | 81 |
| 2014 | 28.4 | 87 |
| 2013 | 27.9 | 94 |
| 2012 | 27.5 | 98 |
| 2011 | 27.2 | 101 |
| 2010 | 27 | 102 |
| 2009 | 27 | 105 |
| 2008 | 27.2 | 109 |
| 2007 | 27.5 | 109 |
| 2006 | 28.1 | 106 |
| 2005 | 28.9 | 105 |
| 2004 | 29.9 | 103 |
| 2003 | 31.1 | 99 |
| 2002 | 32.4 | 94 |
| 2001 | 33.7 | 92 |
| 2000 | 34.8 | 89 |
| 1999 | 35.7 | 86 |
| 1998 | 36.5 | 85 |
| 1997 | 37.1 | 85 |
| 1996 | 37.8 | 84 |
| 1995 | 38.6 | 84 |
| 1994 | 39.1 | 84 |
| 1993 | 39.5 | 84 |
| 1992 | 40 | 83 |
| 1991 | 40.3 | 82 |
| 1990 | 40.5 | 81 |
| 1989 | 40.9 | 78 |
| 1988 | 41.3 | 77 |
| 1987 | 41.7 | 75 |
| 1986 | 41.9 | 75 |