| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 31.76 | 18 |
| 2015 | 30.9 | 36 |
| 2014 | 31.42 | 37 |
| 2013 | 30.2 | 47 |
| 2012 | 29.36 | 49 |
| 2011 | 27.41 | 52 |
| 2010 | 28.29 | 48 |
| 2009 | 29.21 | 44 |
| 2008 | 29.12 | 47 |
| 2007 | 29.76 | 47 |
| 2006 | 27.99 | 49 |
| 2005 | 27.74 | 51 |
| 2004 | 26.54 | 50 |
| 2003 | 25.09 | 48 |
| 2002 | 25.4 | 47 |
| 2001 | 26.47 | 40 |
| 2000 | 28.17 | 36 |
| 1999 | 15.09 | 80 |
| 1998 | 13.97 | 88 |
| 1997 | 13.45 | 84 |
| 1996 | 12.51 | 87 |
| 1995 | 11.8 | 90 |
| 1994 | 11.95 | 86 |
| 1993 | 12.38 | 88 |
| 1992 | 12.02 | 80 |
| 1991 | 11.64 | 79 |
| 1990 | 11.45 | 76 |
| 1989 | 12.15 | 69 |
| 1988 | 12.14 | 66 |
| 1987 | 12.13 | 62 |
| 1986 | 12.05 | 63 |