Year	Percent
1960	56.567
1961	57.303
1962	58.308
1963	59.306
1964	60.298
1965	61.278
1966	62.251
1967	63.214
1968	64.168
1969	65.108
1970	66.038
1971	66.848
1972	67.541
1973	68.224
1974	68.901
1975	69.57
1976	70.231
1977	70.883
1978	71.527
1979	72.162
1980	72.789
1981	73.279
1982	73.515
1983	73.749
1984	73.982
1985	74.213
1986	74.444
1987	74.673
1988	74.9
1989	75.126
1990	75.351
1991	75.528
1992	75.61
1993	75.692
1994	75.774
1995	75.856
1996	75.938
1997	76.019
1998	76.1
1999	76.181
2000	76.262
2001	76.343
2002	76.533
2003	76.778
2004	77.022
2005	77.263
2006	77.502
2007	77.74
2008	77.976
2009	78.21
2010	78.442
2011	78.673
2012	78.902
2013	79.133
2014	79.366
2015	79.602
2016	79.84
2017	80.08