Year Percent 1961 20.89552 1962 20.89552 1963 19.40299 1964 19.40299 1965 19.40299 1966 19.40299 1967 19.40299 1968 17.91045 1969 17.91045 1970 17.91045 1971 14.92537 1972 16.41791 1973 16.41791 1974 13.43284 1975 11.9403 1976 11.9403 1977 11.9403 1978 11.9403 1979 11.9403 1980 11.9403 1981 10.44776 1982 8.95522 1983 8.95522 1984 8.95522 1985 7.46269 1986 5.97015 1987 4.47761 1988 4.47761 1989 2.98507 1990 2.98507 1991 1.79104 1992 1.79104 1993 1.79104 1994 1.79104 1995 1.79104 1996 1.79104 1997 1.79104 1998 1.79104 1999 1.79104 2000 1.79104 2001 1.79104 2002 1.77778 2003 1.16448 2004 1.1611 2005 1.10305 2006 1.08069 2007 1.15108 2008 1 2009 1 2010 1.05413 2011 1.03693 2012 1.03399 2013 0.94767 2014 0.93089 2015 0.93089 2016 0.93089 2017 0.92697 2018 0.92437 2019 0.92179 2020 0.91922 2021 0.91922