Year	Percent
1960	58.534
1961	59.806
1962	61.406
1963	62.983
1964	64.534
1965	66.05
1966	67.491
1967	68.853
1968	70.186
1969	71.481
1970	72.744
1971	73.433
1972	73.675
1973	73.914
1974	74.152
1975	74.389
1976	74.625
1977	74.966
1978	75.355
1979	75.74
1980	76.121
1981	76.497
1982	76.869
1983	77.237
1984	77.602
1985	77.961
1986	78.317
1987	78.668
1988	79.016
1989	79.359
1990	79.698
1991	80.033
1992	80.301
1993	80.503
1994	80.703
1995	80.902
1996	81.1
1997	81.226
1998	81.351
1999	81.476
2000	81.6
2001	81.849
2002	82.095
2003	82.338
2004	82.58
2005	82.858
2006	83.172
2007	83.482
2008	83.787
2009	84.087
2010	84.383
2011	84.755
2012	85.2
2013	85.551
2014	85.813
2015	86.071
2016	86.326
2017	86.574