Year Number 1996 0.421715974807739 1998 0.381433337926865 2000 0.396205484867096 2002 0.392881572246552 2003 0.330509543418884 2004 0.345351129770279 2005 0.352396249771118 2006 0.355119943618774 2007 0.324082791805267 2008 0.325011342763901 2009 0.296177357435226 2010 0.299358755350113 2011 0.332165271043777 2012 0.266220301389694 2013 0.277903288602829 2014 0.227360591292381 2015 0.235534265637398 2016 0.240429624915123 2017 0.249887317419052 2018 0.245429694652557 2019 0.267579674720764 2020 0.264927893877029 2021 0.269547700881958 2022 0.265813022851944