Year % 1998 17.170785687938057 1999 18.25047199496542 2000 16.921658986175117 2001 17.20372359470104 2002 17.874911158493255 2003 16.81230339042295 2004 16.749528544488278 2005 16.86808510638297 2006 17.248829672308236 2007 17.680806675938786 2008 17.97577854671279 2009 18.79621668099742 2010 18.10344827586206 2011 18.087484035759886 2012 18.42857142857142 2013 19.632678910702996 2014 19.282881692002658 2015 20.06417834825201 2016 20.208367785678874 2017 20.51112943116239 2018 21.0586505472962 2019 21.152944852366808 2020 21.901419684160143 2021 21.927221614868024 2022 22.479973297730297 2023 23.310023310023325