| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 3.8 | 31 |
| 2015 | 3.7 | 40 |
| 2014 | 3.6 | 41 |
| 2013 | 3.52 | 47 |
| 2012 | 3.48 | 48 |
| 2011 | 3.47 | 51 |
| 2010 | 3.47 | 53 |
| 2009 | 3.47 | 50 |
| 2008 | 3.43 | 55 |
| 2007 | 3.35 | 58 |
| 2006 | 3.24 | 62 |
| 2005 | 3.14 | 67 |
| 2004 | 3.06 | 66 |
| 2003 | 2.99 | 67 |
| 2002 | 2.94 | 70 |
| 2001 | 2.91 | 68 |
| 2000 | 2.83 | 71 |
| 1999 | 2.79 | 73 |
| 1998 | 2.98 | 75 |
| 1997 | 3.49 | 59 |
| 1996 | 4.26 | 32 |
| 1995 | 5.24 | 11 |
| 1994 | 6.19 | 6 |
| 1993 | 6.82 | 8 |
| 1992 | 6.87 | 9 |
| 1991 | 6.38 | 9 |
| 1990 | 5.6 | 20 |
| 1989 | 4.83 | 36 |
| 1988 | 4.2 | 65 |
| 1987 | 3.89 | 80 |
| 1986 | 3.85 | 80 |