Year	Percent
1960	59.361
1961	59.856
1962	60.355
1963	60.853
1964	61.35
1965	61.843
1966	62.334
1967	62.822
1968	63.309
1969	63.792
1970	64.272
1971	64.75
1972	65.039
1973	65.241
1974	65.442
1975	65.643
1976	65.844
1977	66.044
1978	66.243
1979	66.442
1980	66.64
1981	66.837
1982	66.886
1983	66.866
1984	66.846
1985	66.826
1986	66.806
1987	66.786
1988	66.766
1989	66.746
1990	66.726
1991	66.706
1992	66.742
1993	66.802
1994	66.862
1995	66.922
1996	66.982
1997	67.042
1998	67.102
1999	67.162
2000	67.222
2001	67.282
2002	67.382
2003	67.501
2004	67.62
2005	67.738
2006	67.856
2007	67.974
2008	68.092
2009	68.209
2010	68.327
2011	68.444
2012	68.684
2013	68.979
2014	69.272
2015	69.565
2016	69.855
2017	70.144