Year	Percent
1960	75.998
1961	76.525
1962	77.133
1963	77.73
1964	78.317
1965	78.891
1966	79.421
1967	79.852
1968	80.277
1969	80.695
1970	81.106
1971	81.491
1972	81.819
1973	82.141
1974	82.46
1975	82.774
1976	83.028
1977	83.128
1978	83.229
1979	83.328
1980	83.428
1981	83.511
1982	83.552
1983	83.592
1984	83.633
1985	83.673
1986	83.78
1987	84.025
1988	84.268
1989	84.506
1990	84.742
1991	84.95
1992	85.103
1993	85.254
1994	85.404
1995	85.553
1996	85.7
1997	85.781
1998	85.861
1999	85.941
2000	86.021
2001	86.1
2002	86.161
2003	86.221
2004	86.281
2005	86.341
2006	86.4
2007	86.34
2008	86.28
2009	86.22
2010	86.16
2011	86.1
2012	86.161
2013	86.221
2014	86.281
2015	86.341
2016	86.4
2017	86.466