Year	Percent
1960	74.71
1961	75.102
1962	75.49
1963	75.875
1964	76.255
1965	76.631
1966	77.003
1967	77.37
1968	77.734
1969	78.093
1970	78.448
1971	78.799
1972	79.146
1973	79.488
1974	79.827
1975	80.161
1976	80.491
1977	80.817
1978	81.138
1979	81.456
1980	81.769
1981	82.078
1982	82.383
1983	82.684
1984	82.982
1985	83.274
1986	83.563
1987	83.848
1988	84.129
1989	84.405
1990	84.678
1991	84.947
1992	85.444
1993	86.224
1994	86.969
1995	87.68
1996	88.358
1997	89.002
1998	89.615
1999	90.198
2000	90.752
2001	91.011
2002	90.894
2003	90.775
2004	90.655
2005	90.534
2006	90.411
2007	90.287
2008	90.161
2009	90.034
2010	89.905
2011	89.775
2012	89.654
2013	89.544
2014	89.443
2015	89.352
2016	89.272
2017	89.203