Year Percent 2003 19.62694 2004 20.65959 2005 19.06312 2006 19.14766 2007 18.23539 2008 20.37936 2009 25.67563 2010 20.96879 2011 18.48599 2012 17.20628 2013 16.38971 2014 16.72989