Year % 1979 53.4 1989 61 1991 60.6 1995 60.5 1997 61.3 1998 60.6 1999 59.8 2000 60.1 2001 59.9 2002 59.8 2003 59.5 2004 58.7 2005 57.7 2006 58.4 2007 56.6 2008 57 2009 56.4 2010 56 2011 55.8 2012 56.1 2013 56 2014 54.8 2015 55.3 2016 54.8 2017 54.2 2018 53.6 2019 54.4 2021 55.7 2023 53.5