| Year | Value | | 2019 | 8.6582318495883 | | 2018 | 8.4996437871185 | | 2017 | 10.143713823501 | | 2016 | 7.9259465809177 | | 2015 | 7.1249063196692 | | 2014 | 6.050339842577 | | 2013 | 5.7966112325723 | | 2012 | 5.321685881443 | | 2011 | 5.1859631159796 | | 2010 | 5.1375072826533 | | 2009 | 5.6121414038344 | | 2008 | 4.1946704740237 | | 2007 | 5.6295855195892 | | 2006 | 5.2340098050393 | | 2005 | 5.5481087105495 | | 2004 | 6.72908355722 | | 2003 | 6.7433592126701 | | 2002 | 7.4289585215035 | | 2001 | 6.6771858024539 |
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