Year	Percent
1960	85.275
1961	85.693
1962	86.101
1963	86.5
1964	86.78
1965	87.054
1966	87.323
1967	87.588
1968	87.848
1969	88.103
1970	88.354
1971	88.6
1972	88.678
1973	88.755
1974	88.832
1975	88.909
1976	88.985
1977	89.06
1978	89.135
1979	89.21
1980	89.363
1981	89.514
1982	89.663
1983	89.811
1984	89.956
1985	90.1
1986	90.4
1987	91.056
1988	91.671
1989	92.247
1990	92.786
1991	93.291
1992	93.763
1993	94.203
1994	94.614
1995	94.998
1996	95.356
1997	95.659
1998	95.888
1999	96.105
2000	96.311
2001	96.506
2002	96.692
2003	96.868
2004	97.09
2005	97.396
2006	97.671
2007	97.917
2008	98.139
2009	98.336
2010	98.501
2011	98.602
2012	98.697
2013	98.785
2014	98.868
2015	98.945
2016	99.015
2017	99.078