Year Percent 1985 32.66332 1986 33.05228 1987 30.80645 1988 31.68605 1989 32.02899 1990 33.33333 1991 36.09467 1992 29.52087 1993 20.97983 1994 19.63812 1995 36.69169 1996 36.03593 1997 32.01183 1998 25.10131 1999 25.38864 2000 25.12453 2001 23.80841 2002 22.2321 2003 24.19456 2004 19.22235 2005 21.19169 2006 21.45107 2007 19.43473 2008 19.86728 2009 18.552 2010 19.58668 2011 23.83551 2012 23.32682 2013 21.32089 2014 23.77378 2015 21.59057 2016 20.85698 2017 20.2833 2018 19.77196 2019 20.86707 2020 22.69043 2021 22.44908