| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 16.3 | 20 |
| 2015 | 18.8 | 20 |
| 2014 | 15.3 | 28 |
| 2013 | 18.9 | 25 |
| 2012 | 19.7 | 25 |
| 2011 | 29.3 | 24 |
| 2010 | 46.3 | 19 |
| 2009 | 38.2 | 27 |
| 2008 | 44.3 | 23 |
| 2007 | 55.4 | 25 |
| 2006 | 40.9 | 27 |
| 2005 | 29.7 | 24 |
| 2004 | 22.4 | 29 |
| 2003 | 14 | 31 |
| 2002 | 9.4 | 32 |
| 2001 | 11.5 | 34 |
| 2000 | 21.7 | 28 |
| 1999 | 17.9 | 34 |
| 1998 | 11.9 | 38 |
| 1997 | 12.1 | 34 |
| 1996 | 7.4 | 34 |
| 1995 | 8.8 | 31 |
| 1994 | 33.6 | 10 |
| 1993 | 43.7 | 7 |
| 1992 | 19.9 | 10 |
| 1991 | 14.2 | 11 |
| 1990 | 10 | 16 |
| 1989 | 8.4 | 21 |
| 1988 | 5.3 | 20 |
| 1987 | 13.6 | 14 |
| 1986 | 7.1 | 15 |