Year Number 1996 0.187617555260658 1998 0.302315533161163 2000 0.331546425819397 2002 0.295856952667236 2003 0.361106097698212 2004 0.376263976097107 2005 0.296854168176651 2006 0.24671696126461 2007 0.332813501358032 2008 0.350792974233627 2009 0.276905655860901 2010 0.296465128660202 2011 0.287503004074097 2012 0.275722324848175 2013 0.263921529054642 2014 0.296172291040421 2015 0.330853641033173 2016 0.282597362995148 2017 0.333829998970032 2018 0.330506831407547 2019 0.296385109424591 2020 0.311764776706696 2021 0.311789244413376 2022 0.320023983716965