Year	Percent
1970	62.13235
1971	62.36559
1972	63.15789
1973	63.35616
1974	63.8796
1975	64.16938
1976	64.64968
1977	65.42056
1978	65.6535
1979	66.17211
1980	66.66667
1981	67.13881
1982	67.86704
1983	68.10811
1984	68.78307
1985	69.25065
1986	69.69697
1987	70.12346
1988	70.77295
1989	71.22642
1990	71.82448
1991	72.23476
1992	72.84768
1993	73.43413
1994	73.83966
1995	74.38017
1996	74.79839
1997	75.34517
1998	75.86873
1999	76.22642
2000	76.89464
2001	77.39602
2002	77.69912
2003	78.16291
2004	78.77759
2005	79.06977
2006	79.64169
2007	80.0638
2008	80.46875
2009	80.9816
2010	81.35338
2011	81.85841
2012	82.34443
2013	82.69504
2014	83.14763
2015	83.58413