Year Percent 2003-01-01 15.45 2004-01-01 14.96 2005-01-01 15.36 2006-01-01 15.17 2007-01-01 18.02 2008-01-01 16.10 2009-01-01 17.57 2010-01-01 18.10 2011-01-01 18.37 2012-01-01 18.27 2013-01-01 18.08 2014-01-01 18.49