Year % 1995 31.57 1996 31.6 1997 31.6 1998 31.6 2000 31.6 2001 31.6 2002 31.35 2003 31.35 2004 31.35 2005 31.33 2006 31.35 2007 30.12 2008 30.12 2009 30.12 2010 30.12 2011 30.12 2012 30.66 2013 30.66 2014 30.66 2015 30.66 2016 30.66 2017 30.69 2018 30.69 2019 30.69 2020 30.67 2021 30.69