Year	Percent
1961	59.48373
1962	59.64514
1963	59.80764
1964	59.96904
1965	60.13044
1966	60.18314
1967	59.90535
1968	60.06785
1969	60.33905
1970	60.55535
1971	60.71785
1972	60.87926
1973	61.04066
1974	61.20316
1975	61.36456
1976	61.52596
1977	61.3942
1978	61.51279
1979	61.85096
1980	62.08044
1981	62.19902
1982	62.3187
1983	62.43728
1984	62.77436
1985	63.11363
1986	63.34201
1987	63.43314
1988	63.64285
1989	63.79327
1990	64.46633
1991	65.25797
1992	66.53271
1993	66.92908
1994	67.98423
1995	70.35695
1996	70.53372
1997	70.7094
1998	71.59986
1999	71.76345
2000	71.92595
2001	72.10053
2002	72.25534
2003	72.41894
2004	72.57925
2005	72.74724
2006	72.90205
2007	73.06565
2008	73.23034
2009	73.39175
2010	73.55754
2011	73.72114
2012	73.88583
2013	74.04943
2014	74.21522
2015	74.37333
2016	74.54242
2017	74.70492
2018	74.87291
2019	75.03761
2020	75.2034
2021	75.36919