Year	Percent
1960	66.211
1961	66.641
1962	67.068
1963	67.493
1964	67.916
1965	68.334
1966	68.75
1967	69.163
1968	69.574
1969	69.98
1970	70.384
1971	70.784
1972	71.182
1973	71.576
1974	71.967
1975	72.354
1976	72.739
1977	73.12
1978	73.497
1979	73.871
1980	74.33
1981	75.043
1982	75.743
1983	76.429
1984	77.103
1985	77.762
1986	78.408
1987	79.04
1988	79.659
1989	80.263
1990	80.948
1991	81.886
1992	82.789
1993	83.654
1994	84.485
1995	85.28
1996	86.043
1997	86.771
1998	87.467
1999	88.131
2000	88.587
2001	88.491
2002	88.394
2003	88.297
2004	88.198
2005	88.1
2006	88
2007	87.9
2008	87.799
2009	87.697
2010	87.594
2011	87.502
2012	87.42
2013	87.348
2014	87.288
2015	87.238
2016	87.198
2017	87.17