Year % 2001 19.55 2005 18.56 2007 18.39 2008 18.28 2009 18.24 2010 17.95 2011 17.92 2012 17.44 2013 17.39 2014 17.39 2015 17.47 2016 17.56 2017 19.37 2018 23.32 2019 28.09 2020 23.32 2021 23.24