| Year | Value | | 2016 | 6.0045808232214 | | 2015 | 5.7145594964971 | | 2014 | 6.1044276512967 | | 2013 | 5.0096464534495 | | 2012 | 5.8311660103146 | | 2011 | 12.431549043041 | | 2010 | 6.4453144078066 | | 2009 | 6.448234810667 | | 2008 | 20.470521910996 | | 2007 | 13.149124706298 | | 2006 | 10.010865188646 | | 2005 | 7.0919324408377 | | 2004 | 7.1419650869225 | | 2003 | 16.303491204949 | | 2002 | 12.249984784589 | | 2001 | 38.59188944886 |
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