Year Percent 2002-01-01 18.30 2003-01-01 22.50 2004-01-01 18.80 2005-01-01 16.20 2006-01-01 18.50 2007-01-01 21.00 2008-01-01 23.60 2009-01-01 20.70 2010-01-01 19.70 2011-01-01 20.60 2012-01-01 20.50 2013-01-01 20.89 2014-01-01 20.67 2015-01-01 20.30