Year Number 1996 0.613030731678009 1998 0.575733542442322 2000 0.595203697681427 2002 0.518141508102417 2003 0.349641561508179 2004 0.364736646413803 2005 0.384340941905975 2006 0.376439899206162 2007 0.348420560359955 2008 0.350017130374908 2009 0.293007612228394 2010 0.282069832086563 2011 0.310344904661179 2012 0.278807580471039 2013 0.293446391820908 2014 0.236860454082489 2015 0.24198617041111 2016 0.251646012067795 2017 0.268953740596771 2018 0.258186370134354 2019 0.250075668096542 2020 0.247393816709518 2021 0.248921230435371 2022 0.248592063784599