Year % 2003 26.8 2004 28 2005 29 2006 30.2 2007 29.5 2008 31.8 2009 28.7 2010 26.2 2011 26.8 2012 26.8 2013 25.4 2014 27.8 2015 26.8 2016 27.2 2017 26.1