Year	Percent
1970	61.68421
1971	62.13992
1972	62.5
1973	62.72189
1974	63.12741
1975	63.51607
1976	63.88889
1977	64.24682
1978	64.76868
1979	65.09599
1980	65.47009
1981	65.9396
1982	66.44737
1983	66.88207
1984	67.35341
1985	67.80715
1986	68.24427
1987	68.76877
1988	69.32153
1989	69.85507
1990	70.37037
1991	70.86835
1992	71.4876
1993	72.08672
1994	72.66667
1995	73.35958
1996	74.03101
1997	74.7141
1998	75.46934
1999	76.10837
2000	76.72727
2001	77.32697
2002	78.02585
2003	78.58796
2004	79.15718
2005	79.79798
2006	80.33149
2007	80.84875
2008	81.54506
2009	82.0296
2010	82.60417
2011	83.05955
2012	83.60324
2013	84.13174
2014	84.54724
2015	85.04854