Year % 1997 32.45 1998 32.15 2000 32.15 2001 32.15 2003 29.1 2004 29.1 2005 29.1 2006 29.1 2007 29.24 2008 29.24 2009 29.24 2010 29.24 2011 29.22 2012 29.32 2014 29.32 2015 29.11 2017 29.11 2018 29.13 2019 29.13 2020 29.13 2021 29.13