Year	Percent
1960	50.879
1961	52.412
1962	53.215
1963	53.565
1964	53.914
1965	54.262
1966	54.61
1967	54.957
1968	55.296
1969	55.633
1970	55.971
1971	56.308
1972	56.645
1973	56.98
1974	57.315
1975	57.65
1976	57.984
1977	58.316
1978	58.649
1979	58.98
1980	60.029
1981	61.464
1982	62.882
1983	64.278
1984	65.652
1985	66.996
1986	68.315
1987	69.606
1988	70.868
1989	72.095
1990	73.291
1991	74.455
1992	75.586
1993	76.68
1994	77.74
1995	78.207
1996	78.22
1997	78.232
1998	78.245
1999	78.258
2000	78.27
2001	78.283
2002	78.296
2003	78.308
2004	78.321
2005	79.485
2006	80.97
2007	82.371
2008	83.692
2009	84.928
2010	86.088
2011	87.172
2012	88.185
2013	89.125
2014	90
2015	90.256
2016	90.506
2017	90.747