Year	Percent
1960	76.848
1961	77.985
1962	78.754
1963	79.502
1964	80.232
1965	80.94
1966	81.63
1967	82.3
1968	82.952
1969	83.582
1970	84.195
1971	84.789
1972	85.351
1973	85.793
1974	86.224
1975	86.643
1976	87.053
1977	87.45
1978	87.838
1979	88.215
1980	88.583
1981	88.94
1982	89.287
1983	89.608
1984	89.719
1985	89.828
1986	89.936
1987	90.044
1988	90.15
1989	90.255
1990	90.359
1991	90.463
1992	90.565
1993	90.666
1994	90.767
1995	90.866
1996	90.943
1997	91.009
1998	91.074
1999	91.139
2000	91.203
2001	91.267
2002	91.33
2003	91.393
2004	91.456
2005	91.518
2006	91.58
2007	91.641
2008	91.702
2009	91.763
2010	91.826
2011	91.892
2012	91.96
2013	92.031
2014	92.104
2015	92.179
2016	92.256
2017	92.336