Year % 2000 18.569557245219805 2001 18.214733685578846 2002 18.31379213593916 2003 18.344836340475208 2004 18.11470836048753 2005 17.470057996632303 2006 16.821071902120945 2007 16.292418344283814 2008 15.884703274787217 2009 15.473411333602629 2010 15.13628295060891 2011 14.749214461475201 2012 14.278620672524532 2013 13.86702455118999 2014 13.653838524723135 2015 13.443829326122279 2016 13.304373669870575 2017 13.12106884522833 2018 12.96221621532628 2019 12.836466955027685