| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 23.4 | 113 |
| 2015 | 23.4 | 115 |
| 2014 | 23.6 | 113 |
| 2013 | 23.9 | 113 |
| 2012 | 24.3 | 112 |
| 2011 | 24.8 | 112 |
| 2010 | 25.5 | 111 |
| 2009 | 26.4 | 109 |
| 2008 | 27.4 | 105 |
| 2007 | 28.7 | 101 |
| 2006 | 30.1 | 96 |
| 2005 | 31.6 | 90 |
| 2004 | 33.2 | 84 |
| 2003 | 35 | 79 |
| 2002 | 36.9 | 74 |
| 2001 | 38.8 | 70 |
| 2000 | 40.7 | 60 |
| 1999 | 42.1 | 51 |
| 1998 | 43.4 | 47 |
| 1997 | 44.6 | 35 |
| 1996 | 45.6 | 23 |
| 1995 | 46.5 | 17 |
| 1994 | 47 | 13 |
| 1993 | 47.4 | 11 |
| 1992 | 47.5 | 12 |
| 1991 | 47.5 | 13 |
| 1990 | 47.5 | 11 |
| 1989 | 47.4 | 11 |
| 1988 | 47.3 | 12 |
| 1987 | 47.1 | 14 |
| 1986 | 46.8 | 20 |