Year	Percent
1970	65.29412
1971	66.09195
1972	66.38655
1973	66.84932
1974	67.37968
1975	68.06283
1976	68.5422
1977	69
1978	69.68215
1979	70.09569
1980	70.56075
1981	71.16705
1982	71.81208
1983	72.21007
1984	72.96137
1985	73.52941
1986	74.07407
1987	74.59677
1988	75.09881
1989	75.77519
1990	76.42586
1991	76.86567
1992	77.3309
1993	77.91741
1994	78.48325
1995	79.20277
1996	79.72743
1997	80.23451
1998	80.85809
1999	81.33117
2000	81.81818
2001	82.41758
2002	82.84389
2003	83.28267
2004	83.83234
2005	84.38881
2006	84.78261
2007	85.3067
2008	85.554
2009	86.04972
2010	86.54891
2011	86.8984
2012	87.36842
2013	87.6943
2014	88.26531
2015	88.69347