Year % 1995 19.29 1997 19.3 2001 19.17 2002 19.17 2003 19.36 2004 19.36 2005 19.08 2006 19.2 2007 19.18 2008 19.15 2009 19.15 2010 19.15 2011 19.15 2012 19.24 2013 19.73 2015 19.76 2016 19.76 2017 19.76