Year	Percent
1960	63.272
1961	64.213
1962	65.144
1963	66.064
1964	66.972
1965	67.866
1966	68.704
1967	69.516
1968	70.316
1969	71.102
1970	71.877
1971	72.666
1972	73.452
1973	74.22
1974	74.975
1975	75.716
1976	75.944
1977	76.002
1978	76.06
1979	76.118
1980	76.175
1981	76.273
1982	76.383
1983	76.493
1984	76.603
1985	76.712
1986	76.835
1987	76.962
1988	77.088
1989	77.213
1990	77.339
1991	77.473
1992	77.61
1993	77.746
1994	77.881
1995	78.016
1996	78.145
1997	78.272
1998	78.398
1999	78.523
2000	78.649
2001	79.99
2002	81.647
2003	83.196
2004	84.64
2005	85.978
2006	87.118
2007	88.146
2008	89.103
2009	89.989
2010	90.812
2011	91.069
2012	91.148
2013	91.226
2014	91.304
2015	91.381
2016	91.457
2017	91.535