Year	Percent
1960	56.477
1961	57.864
1962	59.241
1963	60.604
1964	61.952
1965	63.279
1966	64.587
1967	65.874
1968	67.14
1969	68.378
1970	69.592
1971	70.779
1972	71.941
1973	73.07
1974	74.172
1975	75.245
1976	76.288
1977	77.298
1978	78.278
1979	79.228
1980	80.147
1981	81.034
1982	81.891
1983	82.717
1984	83.514
1985	84.28
1986	85.017
1987	85.726
1988	86.407
1989	87.059
1990	87.685
1991	88.285
1992	88.86
1993	89.409
1994	89.934
1995	90.437
1996	90.917
1997	91.374
1998	91.811
1999	92.228
2000	92.586
2001	92.814
2002	93.036
2003	93.251
2004	93.461
2005	93.664
2006	93.861
2007	94.053
2008	94.239
2009	94.419
2010	94.594
2011	94.761
2012	94.919
2013	95.07
2014	95.213
2015	95.35
2016	95.48
2017	95.603