Year	Percent
1960	80.241
1961	80.462
1962	80.681
1963	80.899
1964	81.114
1965	81.328
1966	81.539
1967	81.749
1968	81.958
1969	82.164
1970	82.368
1971	82.57
1972	82.771
1973	82.97
1974	83.167
1975	83.387
1976	83.806
1977	84.215
1978	84.616
1979	85.009
1980	85.394
1981	85.769
1982	86.138
1983	86.498
1984	86.85
1985	87.194
1986	87.558
1987	87.926
1988	88.285
1989	88.633
1990	88.973
1991	89.304
1992	89.627
1993	89.94
1994	90.245
1995	90.542
1996	90.835
1997	91.147
1998	91.45
1999	91.743
2000	92.028
2001	92.303
2002	92.569
2003	92.828
2004	93.078
2005	93.319
2006	93.553
2007	93.779
2008	93.998
2009	94.209
2010	94.414
2011	94.612
2012	94.739
2013	94.843
2014	94.945
2015	95.045
2016	95.144
2017	95.24