Year	Percent
1970	81.6245
1971	82.0915
1972	82.51928
1973	83.05942
1974	83.47826
1975	83.86308
1976	84.3562
1977	84.73373
1978	85.19814
1979	85.64868
1980	85.97285
1981	86.39911
1982	86.7033
1983	87.20174
1984	87.5803
1985	87.85639
1986	88.20459
1987	88.45361
1988	88.78695
1989	89.1129
1990	89.332
1991	89.54635
1992	89.84375
1993	90.03868
1994	90.3164
1995	90.4943
1996	90.66038
1997	90.73901
1998	90.90065
1999	90.97606
2000	91.14155
2001	91.30435
2002	91.55436
2003	91.71123
2004	91.87279
2005	92.03152
2006	92.1875
2007	92.42685
2008	92.66212
2009	92.81488
2010	93.04858
2011	93.27801
2012	93.50329
2013	93.72453
2014	94.02262
2015	94.24