Year	Percent
1960	85.2
1961	85.293
1962	85.582
1963	85.867
1964	86.147
1965	86.422
1966	86.692
1967	86.958
1968	87.22
1969	87.476
1970	87.729
1971	88.039
1972	88.474
1973	88.894
1974	89.301
1975	89.695
1976	90.077
1977	90.445
1978	90.801
1979	91.145
1980	91.478
1981	91.794
1982	92.09
1983	92.376
1984	92.653
1985	92.92
1986	94.248
1987	96.86
1988	98.309
1989	99.094
1990	99.517
1991	99.832
1992	99.979
1993	100
1994	100
1995	100
1996	100
1997	100
1998	100
1999	100
2000	100
2001	100
2002	100
2003	100
2004	100
2005	100
2006	100
2007	100
2008	100
2009	100
2010	100
2011	100
2012	100
2013	100
2014	100
2015	100
2016	100
2017	100