Year	Percent
1970	46.61355
1971	47.08171
1972	47.34848
1973	47.77778
1974	48.37545
1975	48.59155
1976	49.14089
1977	49.66443
1978	50.16393
1979	50.47923
1980	50.9375
1981	51.52439
1982	52.08333
1983	52.61628
1984	52.9745
1985	53.4626
1986	54.05405
1987	54.7619
1988	55.29716
1989	55.80808
1990	56.2963
1991	56.86747
1992	57.54717
1993	58.29493
1994	58.78378
1995	59.47137
1996	60.12931
1997	60.75949
1998	61.23711
1999	62.0202
2000	62.45059
2001	63.05609
2002	63.63636
2003	64.19295
2004	64.79129
2005	65.30249
2006	65.85366
2007	66.38225
2008	67.00168
2009	67.48768
2010	68.11594
2011	68.61199
2012	69.19505
2013	69.75684
2014	70.19374
2015	70.86384