Year % 1995 17.24 1997 17.47 2001 18.93 2002 18.94 2003 24.52 2004 24.52 2005 22.16 2006 24.53 2007 17.43 2008 17.39 2009 17.39 2010 17.39 2011 16.96 2012 18.52 2013 15.97 2015 15.99 2016 15.99 2017 15.99