Year % 1997 40.71 1998 40.5 2000 40.5 2001 40.5 2003 38.15 2004 38.15 2005 38.15 2006 38.15 2007 38.46 2008 38.46 2009 38.46 2010 38.46 2011 38.44 2012 40.67 2014 40.67 2015 40.52 2017 40.52 2018 40.57 2019 40.56 2020 40.56 2021 40.56