| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 7.8 | 4 |
| 2015 | 8 | 7 |
| 2014 | 7.79 | 10 |
| 2013 | 8 | 17 |
| 2012 | 8.2 | 18 |
| 2011 | 8.3 | 22 |
| 2010 | 8.5 | 21 |
| 2009 | 8.1 | 14 |
| 2008 | 9 | 19 |
| 2007 | 9.92 | 27 |
| 2006 | 7.3 | 59 |
| 2005 | 7 | 55 |
| 2004 | 7.7 | 43 |
| 2003 | 4.2 | 96 |
| 2002 | 4 | 76 |
| 2001 | 4.2 | 68 |
| 2000 | 3.8 | 117 |
| 1999 | 4.3 | 69 |
| 1998 | 4.3 | 82 |
| 1997 | 5.2 | 75 |
| 1996 | 1.7 | 149 |
| 1995 | -.9 | 165 |
| 1994 | -5.2 | 168 |
| 1993 | -2.3 | 157 |
| 1992 | -11.2 | 168 |
| 1991 | -.49 | 128 |
| 1990 | 1.6 | 105 |
| 1989 | 3.09 | 99 |
| 1988 | 9.14 | 24 |