Year Percent 1996 36.41086 1997 31.54344 1998 28.78565 1999 25.91875 2000 24.51541 2001 22.71616 2002 22.02511 2003 21.97826 2004 20.53749 2005 18.84531 2006 17.70835 2007 17.15362 2008 16.83705 2009 16.79438 2010 17.95587 2011 18.22679 2012 18.7668 2013 19.56516 2014 19.99018 2015 19.78021 2016 19.84999 2017 19.02213 2018 18.4295 2019 18.38933 2020 19.22522 2021 18.35813 2022 18.62282