| Year | Value | | 2021 | 5.1472331527452 | | 2020 | 0.77988573043673 | | 2019 | 5.3013541791317 | | 2018 | 5.6343868581313 | | 2017 | 5.2081962196156 | | 2016 | 2.657296759818 | | 2015 | 5.9149909549202 | | 2014 | 4.6011945356729 | | 2013 | 1.1691399649353 | | 2012 | 1.7684049229061 | | 2011 | 3.8939686690686 | | 2010 | 1.2444576433997 | | 2009 | 3.8229991875361 | | 2008 | 6.2786837010105 | | 2007 | 7.2825500610054 | | 2006 | 5.0245495453432 | | 2005 | 5.8163195342771 | | 2004 | 3.5820695181145 | | 2003 | 2.1719964896891 | | 2002 | 2.0875482395926 | | 2001 | 1.5895519071513 | | 2000 | 3.2350123893606 | | 1999 | 4.2803353057301 | | 1998 | 5.1676191761983 | | 1997 | 5.9222263779414 | | 1996 | 6.0919686373891 |
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