| 年份 | 2000 | 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 |
| 比例 | 54.6% | 54.9% | 58.1% | 55.4% | 54.1% | 59.8% | 58.2% | 56.2% |
| 年份 | 2008 | 2009 | 2010 | 2011 | 2012 | 2013 | 2014 |
|
| 比例 | 60.0% | 57.1% | 56.7% | 59.2% | 60.5% | 56.8% | 57.8% |
|