Year	Percent
1960	69.996
1961	70.377
1962	70.757
1963	71.134
1964	71.508
1965	71.879
1966	72.247
1967	72.612
1968	72.974
1969	73.333
1970	73.602
1971	73.613
1972	73.623
1973	73.633
1974	73.643
1975	73.653
1976	73.663
1977	73.673
1978	73.682
1979	73.692
1980	73.738
1981	73.89
1982	74.042
1983	74.194
1984	74.344
1985	74.494
1986	74.644
1987	74.793
1988	74.942
1989	75.089
1990	75.3
1991	75.701
1992	76.097
1993	76.488
1994	76.875
1995	77.257
1996	77.636
1997	78.008
1998	78.377
1999	78.742
2000	79.057
2001	79.234
2002	79.409
2003	79.583
2004	79.757
2005	79.928
2006	80.099
2007	80.269
2008	80.438
2009	80.606
2010	80.772
2011	80.944
2012	81.119
2013	81.299
2014	81.483
2015	81.671
2016	81.862
2017	82.058