Year	Percent
1960	46.268
1961	47.702
1962	49.143
1963	50.584
1964	52.027
1965	52.82
1966	53.587
1967	54.352
1968	55.117
1969	55.877
1970	56.635
1971	57.39
1972	58.143
1973	58.89
1974	59.607
1975	60.306
1976	61.003
1977	61.693
1978	62.379
1979	63.061
1980	63.738
1981	64.408
1982	65.073
1983	65.733
1984	66.387
1985	67.034
1986	67.566
1987	68.051
1988	68.532
1989	69.008
1990	69.481
1991	69.949
1992	70.415
1993	70.874
1994	71.328
1995	71.777
1996	72.223
1997	72.662
1998	73.098
1999	73.53
2000	73.957
2001	74.379
2002	74.797
2003	75.211
2004	75.62
2005	76.024
2006	76.423
2007	76.816
2008	77.204
2009	77.587
2010	77.964
2011	78.335
2012	78.701
2013	79.061
2014	79.415
2015	79.764
2016	80.108
2017	80.446