Year	Percent
1960	74.893
1961	75.787
1962	76.66
1963	77.511
1964	78.341
1965	79.273
1966	80.716
1967	82.081
1968	83.371
1969	84.582
1970	85.661
1971	86.444
1972	87.192
1973	87.902
1974	88.579
1975	89.384
1976	90.745
1977	91.944
1978	93
1979	93.928
1980	94.781
1981	95.67
1982	96.414
1983	97.034
1984	97.551
1985	97.903
1986	97.917
1987	97.932
1988	97.946
1989	97.96
1990	97.974
1991	97.988
1992	98.002
1993	98.016
1994	98.029
1995	98.096
1996	98.325
1997	98.527
1998	98.705
1999	98.862
2000	99
2001	99.908
2002	100
2003	100
2004	100
2005	100
2006	100
2007	100
2008	100
2009	100
2010	100
2011	100
2012	100
2013	100
2014	100
2015	100
2016	100
2017	100