Year	Percent
1970	65.83144
1971	66.36971
1972	66.95652
1973	67.44681
1974	68.125
1975	68.63544
1976	69.32271
1977	69.78558
1978	70.61069
1979	71.21495
1980	71.84644
1981	72.45081
1982	73.02977
1983	73.75643
1984	74.45378
1985	75.2883
1986	75.80645
1987	76.74051
1988	77.36434
1989	78.1155
1990	78.83756
1991	79.67836
1992	80.37249
1993	81.29395
1994	82.18232
1995	82.92683
1996	83.75499
1997	84.31373
1998	85.08997
1999	85.73232
2000	86.58385
2001	87.17949
2002	87.7551
2003	88.31169
2004	89.06977
2005	89.5881
2006	90.09009
2007	90.68736
2008	91.15721
2009	91.81916
2010	92.25875
2011	92.68548
2012	93.20288
2013	93.60406
2014	93.99399
2015	94.4664