Year Percent 2006-01-01 17.90 2007-01-01 21.30 2008-01-01 23.30 2009-01-01 22.00 2010-01-01 20.00 2011-01-01 20.10 2012-01-01 18.30 2013-01-01 16.90 2014-01-01 16.20 2015-01-01 15.59