Year Number 1996 0.386360377073288 1998 0.440841853618622 2000 0.416249960660934 2002 0.366997271776199 2003 0.276095181703568 2004 0.255683898925781 2005 0.195907831192017 2006 0.266140520572662 2007 0.300675332546234 2008 0.285400986671448 2009 0.264090776443481 2010 0.266628265380859 2011 0.268976420164108 2012 0.263500511646271 2013 0.260215818881989 2014 0.273231506347656 2015 0.267593652009964 2016 0.29967126250267 2017 0.279159247875214 2018 0.283440768718719 2019 0.284593105316162 2020 0.306642383337021 2021 0.334155827760696 2022 0.324080735445023