Year Percent 2000 26 2001 28 2002 27 2003 27 2004 27 2005 27 2006 28 2007 28 2008 31 2009 33 2010 32 2011 34 2012 33 2013 34 2014 33 2015 32 2016 32 2017 32 2018 32 2019 34 2020 29