Year	Percent
1960	61.613
1961	62.875
1962	63.933
1963	64.977
1964	66.009
1965	67.022
1966	68.022
1967	69.005
1968	69.973
1969	70.92
1970	71.852
1971	72.764
1972	73.575
1973	74.325
1974	75.063
1975	75.786
1976	76.496
1977	77.189
1978	77.868
1979	78.533
1980	79.185
1981	79.82
1982	80.382
1983	80.907
1984	81.422
1985	81.925
1986	82.418
1987	82.9
1988	83.372
1989	83.833
1990	84.284
1991	84.664
1992	85.012
1993	85.352
1994	85.686
1995	86.014
1996	86.336
1997	86.65
1998	86.959
1999	87.262
2000	87.559
2001	87.85
2002	87.876
2003	87.902
2004	87.928
2005	87.954
2006	87.98
2007	88.006
2008	88.031
2009	88.057
2010	88.083
2011	88.108
2012	88.123
2013	88.133
2014	88.144
2015	88.154
2016	88.165
2017	88.183