Year Number 1996 0.187617555260658 1998 0.302315533161163 2000 0.331546425819397 2002 0.295856952667236 2003 0.361106097698212 2004 0.410197407007217 2005 0.30711555480957 2006 0.435252577066422 2007 0.469166576862335 2008 0.451515167951584 2009 0.323029518127441 2010 0.335227936506271 2011 0.329279899597168 2012 0.313144892454147 2013 0.300637990236282 2014 0.350605726242065 2015 0.330853641033173 2016 0.3202865421772 2017 0.333829998970032 2018 0.330506831407547 2019 0.328059256076813 2020 0.357047557830811 2021 0.362440079450607 2022 0.361435800790787