Year % 2001 14.7 2002 14.37 2003 15.54 2004 15.27 2005 15.69 2006 16.53 2007 16.8 2008 15.97 2009 17.18 2010 15.12 2011 17.41 2012 15.47 2013 15.81 2015 16.75 2017 15.79 2018 15.12