Year Percent 2005-01-01 40.1 2006-01-01 39.9 2007-01-01 39.8 2008-01-01 39.7 2009-01-01 39.9 2010-01-01 40.1 2011-01-01 40.2 2012-01-01 40.1 2013-01-01 40.2 2014-01-01 40.3 2015-01-01 40.3 2016-01-01 40.0