Year	Percent
1960	73.5
1961	74.383
1962	75.248
1963	76.093
1964	76.919
1965	77.723
1966	78.508
1967	79.272
1968	79.8
1969	79.8
1970	79.8
1971	79.8
1972	79.8
1973	79.8
1974	79.8
1975	79.8
1976	79.903
1977	80.106
1978	80.309
1979	80.51
1980	80.71
1981	80.683
1982	80.466
1983	80.247
1984	80.026
1985	79.804
1986	79.624
1987	79.482
1988	79.339
1989	79.196
1990	79.051
1991	78.906
1992	78.76
1993	78.614
1994	78.467
1995	78.319
1996	78.493
1997	78.938
1998	79.378
1999	79.81
2000	80.236
2001	80.655
2002	81.067
2003	81.472
2004	81.871
2005	82.262
2006	82.648
2007	83.023
2008	83.387
2009	83.742
2010	84.087
2011	84.423
2012	84.749
2013	85.066
2014	85.375
2015	85.674
2016	85.965
2017	86.248