| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 33.6 | 59 |
| 2015 | 34.1 | 59 |
| 2014 | 34.6 | 59 |
| 2013 | 35.1 | 59 |
| 2012 | 35.7 | 58 |
| 2011 | 36.3 | 57 |
| 2010 | 36.9 | 57 |
| 2009 | 37.3 | 57 |
| 2008 | 37.7 | 58 |
| 2007 | 38.1 | 57 |
| 2006 | 38.4 | 58 |
| 2005 | 38.8 | 59 |
| 2004 | 39.2 | 59 |
| 2003 | 39.5 | 60 |
| 2002 | 39.8 | 62 |
| 2001 | 40.1 | 64 |
| 2000 | 40.3 | 66 |
| 1999 | 41.1 | 60 |
| 1998 | 41.8 | 58 |
| 1997 | 42.5 | 53 |
| 1996 | 43 | 50 |
| 1995 | 43.5 | 49 |
| 1994 | 43.9 | 50 |
| 1993 | 44.1 | 53 |
| 1992 | 44 | 54 |
| 1991 | 44 | 55 |
| 1990 | 44.1 | 54 |
| 1989 | 44.3 | 52 |
| 1988 | 44.7 | 50 |
| 1987 | 45.1 | 47 |
| 1986 | 45.4 | 43 |