| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 28.4 | 84 |
| 2015 | 28.6 | 85 |
| 2014 | 28.6 | 84 |
| 2013 | 28.5 | 87 |
| 2012 | 28.4 | 92 |
| 2011 | 28.4 | 94 |
| 2010 | 28.4 | 96 |
| 2009 | 28.7 | 96 |
| 2008 | 28.9 | 97 |
| 2007 | 29.3 | 97 |
| 2006 | 29.6 | 99 |
| 2005 | 30.1 | 98 |
| 2004 | 30.7 | 99 |
| 2003 | 31.4 | 97 |
| 2002 | 32.2 | 97 |
| 2001 | 33 | 97 |
| 2000 | 33.8 | 96 |
| 1999 | 34.6 | 96 |
| 1998 | 35.3 | 93 |
| 1997 | 36.1 | 89 |
| 1996 | 36.8 | 88 |
| 1995 | 37.6 | 87 |
| 1994 | 38.5 | 86 |
| 1993 | 39.4 | 85 |
| 1992 | 40.2 | 82 |
| 1991 | 41.1 | 76 |
| 1990 | 41.7 | 73 |
| 1989 | 42.5 | 69 |
| 1988 | 43.1 | 64 |
| 1987 | 43.7 | 61 |
| 1986 | 44.3 | 57 |