| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 31.9 | 24 |
| 2015 | 30.9 | 23 |
| 2014 | 26.6 | 33 |
| 2013 | 37.4 | 21 |
| 2012 | 34.1 | 23 |
| 2011 | 45.9 | 27 |
| 2010 | 47.2 | 27 |
| 2009 | 52.7 | 26 |
| 2008 | 95.5 | 26 |
| 2007 | 70.7 | 20 |
| 2006 | 48.4 | 23 |
| 2005 | 45.3 | 22 |
| 2004 | 50.9 | 22 |
| 2003 | 63.5 | 16 |
| 2002 | 62.1 | 15 |
| 2001 | 61.5 | 21 |
| 2000 | 62.3 | 22 |
| 1999 | 55.7 | 17 |
| 1998 | 61.6 | 18 |
| 1997 | 71 | 12 |
| 1996 | 40.2 | 19 |
| 1995 | 43.2 | 13 |
| 1994 | 66.3 | 9 |
| 1993 | 62.9 | 7 |
| 1992 | 38.6 | 10 |
| 1991 | 38 | 8 |
| 1990 | 61.5 | 8 |
| 1989 | 39.3 | 12 |
| 1988 | 19.2 | 17 |
| 1987 | 40.4 | 12 |
| 1986 | 16.1 | 19 |