Year	Percent
1961	69.44758
1962	67.75648
1963	68.20744
1964	65.95265
1965	68.6584
1966	65.50169
1967	64.03608
1968	63.8106
1969	63.35964
1970	62.23224
1971	59.75197
1972	58.06088
1973	55.46787
1974	55.69335
1975	55.58061
1976	55.58061
1977	55.35513
1978	55.80609
1979	54.79143
1980	53.5513
1981	52.64938
1982	52.64938
1983	52.53664
1984	52.31116
1985	51.97294
1986	52.19842
1987	52.08568
1988	52.08568
1989	50.73281
1990	49.04171
1991	47.35062
1992	46.22322
1993	35.06201
1994	34.83653
1995	34.83653
1996	34.83653
1997	32.80722
1998	30.72153
1999	29.30101
2000	27.86922
2001	26.45998
2002	25.02818
2003	24.30665
2004	23.56257
2005	22.81849
2006	22.07441
2007	21.30778
2008	21.49944
2009	21.67982
2010	21.8602
2011	22.04059
2012	22.18715
2013	21.66855
2014	21.14994
2015	20.63134
2016	20.11274
2017	19.59414
2018	19.04171
2019	19.04171
2020	19.04171
2021	19.04171