Year Percent 2004-01-01 7.28 2005-01-01 8.05 2006-01-01 8.92 2007-01-01 10.68 2008-01-01 10.45 2009-01-01 11.61 2010-01-01 12.29 2011-01-01 12.37 2012-01-01 13.59 2013-01-01 13.88 2014-01-01 15.70 2015-01-01 17.68 2016-01-01 20.26