Year	Percent
1960	92.46
1961	92.554
1962	92.679
1963	92.835
1964	92.988
1965	93.137
1966	93.284
1967	93.428
1968	93.569
1969	93.707
1970	93.843
1971	93.976
1972	94.106
1973	94.233
1974	94.358
1975	94.48
1976	94.6
1977	94.806
1978	95.005
1979	95.196
1980	95.381
1981	95.535
1982	95.637
1983	95.737
1984	95.835
1985	95.93
1986	96.023
1987	96.115
1988	96.204
1989	96.292
1990	96.377
1991	96.461
1992	96.542
1993	96.622
1994	96.7
1995	96.777
1996	96.851
1997	96.924
1998	96.996
1999	97.065
2000	97.129
2001	97.186
2002	97.241
2003	97.296
2004	97.35
2005	97.403
2006	97.454
2007	97.505
2008	97.555
2009	97.603
2010	97.651
2011	97.698
2012	97.744
2013	97.789
2014	97.833
2015	97.876
2016	97.919
2017	97.961