Year Percent 2006-01-01 15.3306132272467 2007-01-01 15.4300346718835 2008-01-01 15.9291832118179 2009-01-01 16.5094130492796 2010-01-01 17.8732974294880 2011-01-01 19.1093446628516 2012-01-01 19.7417094220682 2013-01-01 20.4150287226415 2014-01-01 20.2628475762550