2021 3.34 2020 3.11 2019 2.82 2018 2.53 2017 2.51 2016 2.37 2015 2.28 2014 1.77 2013 1.66 2012 1.65 2011 1.69 2010 1.78 2009 1.67 2008 1.49 2007 1.66 2006 1.78 2005 1.81