Year Percent 1991 52.243 1992 51.427 1993 50.975 1994 51.317 1995 51.635 1996 51.493 1997 52.003 1998 53.082 1999 53.966 2000 54.722 2001 54.906 2002 55.847 2003 56.77 2004 57.057 2005 56.992 2006 57.471 2007 58.392 2008 58.484 2009 57.543 2010 57.379 2011 57.284 2012 57.415 2013 57.616 2014 57.186 2015 56.949 2016 57.013 2017 57.139 2018 57.275 2019 57.122 2020 56.96 2021 56.79 2022 56.604