| Year | Value | | 2020 | 8.3244844020754 | | 2019 | 7.101549608696 | | 2018 | 6.8284523184973 | | 2017 | 10.135263083183 | | 2016 | 12.913134199463 | | 2015 | 12.195144417555 | | 2014 | 9.5809211561453 | | 2013 | 8.6243607645102 | | 2012 | 7.278246335806 | | 2011 | 8.1144897699896 | | 2010 | 6.9029386461302 | | 2009 | 8.2238818895365 | | 2008 | 5.8966245476908 | | 2007 | 6.0275738171486 | | 2006 | 5.295008819877 | | 2005 | 5.6881204354828 | | 2004 | 7.8135944063442 | | 2003 | 8.647504675657 | | 2002 | 8.1429046510523 | | 2001 | 9.0709368744813 |
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