Year Number 1996 0.187617555260658 1998 0.302315533161163 2000 0.331546425819397 2002 0.295856952667236 2003 0.361106097698212 2004 0.376263976097107 2005 0.2796431183815 2006 0.355723708868027 2007 0.361441880464554 2008 0.357565850019455 2009 0.34416800737381 2010 0.345248699188232 2011 0.34813866019249 2012 0.337194293737412 2013 0.330278247594833 2014 0.371752977371216 2015 0.393420308828354 2016 0.385219007730484 2017 0.392407566308975 2018 0.388508200645447 2019 0.394042789936066 2020 0.433770954608917 2021 0.423158824443817 2022 0.415553271770477