Year	Percent
1961	59.49862
1962	59.49455
1963	59.39687
1964	59.2992
1965	59.2056
1966	59.10793
1967	59.01026
1968	58.91258
1969	58.81491
1970	58.72131
1971	58.62364
1972	58.52596
1973	58.42829
1974	58.33469
1975	58.27771
1976	58.18004
1977	58.08237
1978	57.9847
1979	57.97249
1980	57.87482
1981	57.77714
1982	57.67947
1983	57.6225
1984	57.52889
1985	57.47192
1986	57.37425
1987	57.27657
1988	57.30506
1989	57.20739
1990	57.54924
1991	57.17483
1992	57.19925
1993	57.18704
1994	57.17076
1995	57.07309
1996	57.11786
1997	57.12193
1998	57.24809
1999	57.29285
2000	57.29692
2001	57.30099
2002	57.34576
2003	57.43122
2004	57.47599
2005	57.46785
2006	57.50448
2007	57.70796
2008	57.95214
2009	57.99284
2010	58.19632
2011	58.19632
2012	58.60329
2013	59.01026
2014	59.14455
2015	59.19339
2016	59.27478
2017	59.39687
2018	59.50676
2019	59.53931
2020	59.55966
2021	59.57187