Year	Percent
1970	48.54881
1971	48.96907
1972	49.37028
1973	49.75369
1974	50.12048
1975	50.35294
1976	50.92166
1977	51.35135
1978	51.54185
1979	52.15517
1980	52.53165
1981	52.78351
1982	53.33333
1983	53.75494
1984	54.15861
1985	54.64896
1986	55.01859
1987	55.45455
1988	55.97148
1989	56.46853
1990	56.84932
1991	57.31092
1992	57.82537
1993	58.31987
1994	58.79556
1995	59.2535
1996	59.78593
1997	60.36036
1998	60.76696
1999	61.30435
2000	61.82336
2001	62.23776
2002	62.86107
2003	63.46414
2004	63.96277
2005	64.5288
2006	64.99356
2007	65.56962
2008	66.00249
2009	66.62577
2010	67.27053
2011	67.77646
2012	68.30409
2013	68.7788
2014	69.46652
2015	70.02237