Year Percent 2003 37.79544 2004 39.22924 2005 41.06066 2006 37.80312 2007 36.20226 2008 36.97913 2009 30.73112 2010 34.05597 2011 37.99793 2012 37.51199 2013 37.91887 2014 38.53128 2015 37.0831 2016 38.98097