Year % 2006 20.1 2007 18.4 2008 17 2009 16.8 2010 17.9 2011 18.2 2012 18.9 2013 20.9 2014 21.3 2015 20.5 2016 18.8 2017 19.2 2018 18.1 2019 18 2020 18 2021 17