Year	Percent
1970	62.58065
1971	62.89308
1972	63.38462
1973	63.96396
1974	64.22287
1975	64.57143
1976	65.0838
1977	65.84699
1978	66.13333
1979	66.66667
1980	66.92112
1981	67.41294
1982	68.12652
1983	68.40855
1984	68.90951
1985	69.54545
1986	70
1987	70.282
1988	70.91295
1989	71.36929
1990	71.80527
1991	72.42063
1992	72.81553
1993	73.38403
1994	73.79182
1995	74.49909
1996	74.91103
1997	75.47826
1998	76.02041
1999	76.5391
2000	77.03583
2001	77.54777
2002	78.00312
2003	78.59327
2004	79.04192
2005	79.47214
2006	80.14388
2007	80.53597
2008	81.05118
2009	81.54681
2010	82
2011	82.59162
2012	83.03342
2013	83.4596
2014	83.99504
2015	84.39024