Year	Percent
1960	46.811
1961	47.398
1962	48.514
1963	49.632
1964	50.752
1965	51.868
1966	52.983
1967	54.096
1968	55.207
1969	56.309
1970	57.406
1971	58.496
1972	59.547
1973	60.188
1974	60.827
1975	61.461
1976	62.093
1977	62.719
1978	63.341
1979	63.96
1980	64.574
1981	65.182
1982	65.61
1983	66.031
1984	66.449
1985	66.864
1986	67.277
1987	67.687
1988	68.095
1989	68.499
1990	68.901
1991	69.3
1992	69.697
1993	70.089
1994	70.521
1995	70.951
1996	71.377
1997	71.798
1998	72.216
1999	72.631
2000	73.042
2001	73.448
2002	73.85
2003	74.249
2004	74.644
2005	75.034
2006	75.421
2007	75.803
2008	76.052
2009	76.241
2010	76.43
2011	76.617
2012	76.804
2013	76.989
2014	77.173
2015	77.357
2016	77.539
2017	77.72