2019 4 2018 4.05 2017 4.3 2016 3.55 2015 3.74 2014 4.67 2013 5.22 2012 5.32 2011 5.74 2010 5.87 2009 5.26 2008 0.06 2007 0.07 2006 0.07 2005 0.06