| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 27.6 | 93 |
| 2015 | 27.7 | 94 |
| 2014 | 27.8 | 95 |
| 2013 | 27.9 | 95 |
| 2012 | 28 | 93 |
| 2011 | 28.2 | 96 |
| 2010 | 28.5 | 95 |
| 2009 | 28.8 | 95 |
| 2008 | 29.3 | 94 |
| 2007 | 29.8 | 94 |
| 2006 | 30.3 | 94 |
| 2005 | 30.8 | 94 |
| 2004 | 31.3 | 93 |
| 2003 | 31.8 | 94 |
| 2002 | 32.2 | 96 |
| 2001 | 32.8 | 99 |
| 2000 | 33.5 | 98 |
| 1999 | 34.2 | 97 |
| 1998 | 35 | 97 |
| 1997 | 35.8 | 94 |
| 1996 | 36.5 | 90 |
| 1995 | 37.1 | 89 |
| 1994 | 37.8 | 88 |
| 1993 | 38.3 | 88 |
| 1992 | 38.7 | 88 |
| 1991 | 39.2 | 86 |
| 1990 | 39.7 | 85 |
| 1989 | 40.1 | 83 |
| 1988 | 40.5 | 83 |
| 1987 | 41 | 81 |
| 1986 | 41.3 | 80 |