Year	Percent
1960	69.556
1961	69.927
1962	70.443
1963	70.953
1964	71.459
1965	71.958
1966	72.452
1967	72.941
1968	73.425
1969	73.902
1970	74.374
1971	74.916
1972	75.528
1973	76.127
1974	76.717
1975	77.297
1976	77.867
1977	78.426
1978	78.975
1979	79.513
1980	80.042
1981	80.444
1982	80.501
1983	80.557
1984	80.613
1985	80.669
1986	80.725
1987	80.78
1988	80.836
1989	80.891
1990	80.947
1991	81.13
1992	81.528
1993	81.857
1994	82.482
1995	82.893
1996	82.825
1997	82.779
1998	82.893
1999	83.448
2000	84.216
2001	84.843
2002	85.299
2003	85.743
2004	86.177
2005	86.598
2006	87.009
2007	87.409
2008	87.8
2009	88.178
2010	88.547
2011	88.906
2012	89.249
2013	89.574
2014	89.884
2015	90.179
2016	90.46
2017	90.727