Year	Percent
1960	55.911
1961	56.335
1962	56.758
1963	57.181
1964	57.603
1965	58.022
1966	58.441
1967	58.859
1968	59.276
1969	59.691
1970	60.112
1971	60.539
1972	60.965
1973	61.388
1974	61.81
1975	62.231
1976	62.65
1977	63.066
1978	63.48
1979	63.893
1980	64.191
1981	64.372
1982	64.553
1983	64.734
1984	64.915
1985	65.095
1986	65.274
1987	65.453
1988	65.632
1989	65.81
1990	65.838
1991	65.713
1992	65.587
1993	65.461
1994	65.335
1995	65.209
1996	65.083
1997	64.956
1998	64.829
1999	64.702
2000	64.575
2001	64.67
2002	65.081
2003	65.489
2004	65.896
2005	66.365
2006	66.895
2007	67.421
2008	67.943
2009	68.46
2010	68.911
2011	69.358
2012	69.678
2013	69.953
2014	70.227
2015	70.5
2016	70.779
2017	71.062