Year Number 1996 1.60150218009949 1998 1.65966057777405 2000 1.79679453372955 2002 1.85915970802307 2003 1.91875457763672 2004 1.90612423419952 2005 1.93932402133942 2006 1.88209331035614 2007 1.82779610157013 2008 1.8531905412674 2009 1.70691537857056 2010 1.70661580562592 2011 1.68856692314148 2012 1.67797338962555 2013 1.65392100811005 2014 1.70472538471222 2015 1.6339955329895 2016 1.48363721370697 2017 1.5700169801712 2018 1.67916393280029 2019 1.72634088993073 2020 1.75132393836975 2021 1.712641954422 2022 1.70302581787109