Year	Percent
1960	72.49
1961	73.295
1962	74.271
1963	75.223
1964	76.153
1965	77.056
1966	77.914
1967	78.727
1968	79.519
1969	80.287
1970	81.034
1971	81.563
1972	81.886
1973	82.203
1974	82.517
1975	82.73
1976	82.802
1977	82.873
1978	82.944
1979	83.016
1980	83.087
1981	83.1
1982	83.1
1983	83.1
1984	83.1
1985	83.1
1986	83.1
1987	83.1
1988	83.1
1989	83.1
1990	83.1
1991	83.204
1992	83.361
1993	83.516
1994	83.671
1995	83.824
1996	83.914
1997	83.942
1998	83.97
1999	83.998
2000	84.026
2001	84.071
2002	84.133
2003	84.196
2004	84.258
2005	84.319
2006	84.43
2007	84.588
2008	84.746
2009	84.902
2010	85.056
2011	85.297
2012	85.62
2013	85.936
2014	86.247
2015	86.553
2016	86.852
2017	87.146