Year Percent 2001 22.50245 2002 22.54575 2003 22.12972 2004 19.97845 2005 20.16686 2006 19.27051 2007 25.09362 2008 25.09813 2009 31.63348 2010 27.08185 2011 23.19026 2012 21.91215 2013 19.28567 2014 22.19793 2015 25.67137 2016 26.02948 2017 24.81162