Year % 2004 30.1 2005 30.3 2006 31.1 2007 31.1 2008 31.7 2009 32.1 2010 31.5 2011 32.6 2012 34.3 2013 37 2014 35.6 2015 34 2016 32.9 2017 31.4 2018 32.7 2019 31.2 2020 31.7 2021 31.3