| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 13.2 | 35 |
| 2015 | 12.2 | 36 |
| 2014 | 11.6 | 43 |
| 2013 | 13.4 | 39 |
| 2012 | 10.1 | 41 |
| 2009 | 9.3 | 52 |
| 2008 | 13.6 | 53 |
| 2007 | 12.5 | 50 |
| 2006 | 12.1 | 46 |
| 2005 | 13.4 | 44 |
| 2004 | 11.6 | 45 |
| 2003 | 11.7 | 41 |
| 2002 | 11.9 | 38 |
| 2001 | 47.7 | 23 |
| 2000 | 53.6 | 25 |
| 1999 | 42.5 | 23 |
| 1998 | 47.5 | 23 |
| 1997 | 29 | 34 |
| 1996 | 25.3 | 28 |
| 1995 | 26.7 | 27 |
| 1994 | 27.3 | 23 |
| 1993 | 26.3 | 21 |
| 1992 | 19.7 | 21 |
| 1991 | 18.9 | 20 |
| 1990 | 21.8 | 20 |
| 1989 | 7 | 25 |
| 1988 | 8 | 24 |
| 1987 | 18.7 | 21 |
| 1986 | 9.7 | 23 |