Year	Percent
1960	80.3
1961	80.803
1962	81.297
1963	81.781
1964	82.256
1965	82.72
1966	83.175
1967	83.621
1968	84.057
1969	84.483
1970	84.9
1971	85.269
1972	85.63
1973	85.983
1974	86.33
1975	86.669
1976	87.002
1977	87.326
1978	87.644
1979	87.955
1980	88.26
1981	88.533
1982	88.8
1983	89.062
1984	89.319
1985	89.57
1986	89.816
1987	90.057
1988	90.294
1989	90.524
1990	90.75
1991	90.932
1992	91.112
1993	91.287
1994	91.46
1995	91.63
1996	91.797
1997	91.96
1998	92.121
1999	92.267
2000	92.401
2001	92.532
2002	92.662
2003	92.789
2004	92.914
2005	93.037
2006	93.159
2007	93.278
2008	93.395
2009	93.511
2010	93.574
2011	93.587
2012	93.6
2013	93.633
2014	93.667
2015	93.7
2016	93.735
2017	93.773