Year Percent 2007-01-01 15.54 2008-01-01 13.04 2009-01-01 14.78 2010-01-01 14.35 2011-01-01 15.46 2012-01-01 13.43 2013-01-01 13.34 2014-01-01 14.30 2015-01-01 13.93