Year Percent 2000 26.96 2001 27.76 2002 28.37 2003 27.85 2004 28.79 2005 28.41 2006 28.41 2007 28.33 2008 25.76 2009 25.25 2010 24.39 2011 24.17 2012 23.44 2013 23.51 2014 23.42 2015 23.82 2016 23.33 2017 23.29