Year	Percent
1961	68.03614
1962	67.75178
1963	67.44372
1964	66.87796
1965	66.56694
1966	66.59064
1967	66.40107
1968	66.19372
1969	65.70498
1970	65.20438
1971	63.28199
1972	62.84656
1973	62.44076
1974	62.17713
1975	61.82168
1976	61.60841
1977	61.19076
1978	60.73164
1979	60.33175
1980	60.3436
1981	60.14514
1982	60.05332
1983	59.50237
1984	59.68306
1985	59.8282
1986	59.77488
1987	59.66528
1988	59.69787
1989	59.41647
1990	59.77488
1991	58.33827
1992	58.16943
1993	58.26126
1994	57.77251
1995	58.19609
1996	57.77844
1997	58.15462
1998	56.74763
1999	58.43009
2000	58.04502
2001	56.95201
2002	57.46742
2003	56.68543
2004	57.74289
2005	57.39633
2006	56.86019
2007	56.70616
2008	57.14751
2009	56.84554
2010	55.50845
2011	55.11269
2012	54.61744
2013	54.8412
2014	54.5889
2015	54.82625
2016	53.90555
2017	54.02435
2018	54.14315
2019	53.95901
2020	53.88922
2021	53.81645