Year Number 1996 -2.68281292915344 1998 -2.84785175323486 2000 -2.47423815727234 2002 -1.97592794895172 2003 -2.02786993980408 2004 -2.38776421546936 2005 -2.12856149673462 2006 -2.24673223495483 2007 -2.1784999370575 2008 -2.00307631492615 2009 -2.00098276138306 2010 -2.19674205780029 2011 -2.21298933029175 2012 -2.08589291572571 2013 -2.19219064712524 2014 -2.16792130470276 2015 -2.1388533115387 2016 -2.22458934783936 2017 -2.33943891525269 2018 -2.0807466506958 2019 -1.62443852424622 2020 -1.78548359870911 2021 -1.65781247615814 2022 -1.97774624824524