Year Percent 1990 0.54829 1991 0.50646 1992 0.46866 1993 0.46275 1994 0.45586 1995 1.65478 1996 1.63061 1997 1.25024 1998 1.1915 1999 0.43086 2000 0.38689 2001 0.35458 2002 0.31105 2003 0.28313 2004 0.27449 2005 0.27486 2006 0.49762 2007 0.29497 2008 0.29056 2009 0.36586 2010 0.38594 2011 0.36846 2012 0.29175 2013 0.35588 2014 0.37418 2015 0.35531 2016 0.34742 2017 0.33647 2018 0.37713 2019 0.37278 2020 0.3883