Year	Percent
1960	59.712
1961	60.454
1962	61.193
1963	61.926
1964	62.642
1965	63.343
1966	64.04
1967	64.73
1968	65.416
1969	66.093
1970	66.764
1971	67.429
1972	68.088
1973	68.738
1974	69.381
1975	70.017
1976	70.647
1977	71.266
1978	71.879
1979	72.484
1980	73.102
1981	73.843
1982	74.571
1983	75.285
1984	75.987
1985	76.674
1986	77.347
1987	78.007
1988	78.654
1989	79.284
1990	79.838
1991	80.067
1992	80.293
1993	80.518
1994	80.74
1995	80.961
1996	81.18
1997	81.396
1998	81.611
1999	81.824
2000	82.007
2001	82.049
2002	82.092
2003	82.134
2004	82.176
2005	82.218
2006	82.26
2007	82.302
2008	82.343
2009	82.385
2010	82.427
2011	82.476
2012	82.532
2013	82.596
2014	82.668
2015	82.746
2016	82.832
2017	82.925