Year	Percent
1960	67.836
1961	68.66
1962	69.435
1963	70.2
1964	70.955
1965	71.696
1966	72.427
1967	73.146
1968	73.854
1969	74.547
1970	75.227
1971	75.883
1972	76.528
1973	77.159
1974	77.778
1975	78.386
1976	78.982
1977	79.565
1978	80.136
1979	80.695
1980	81.243
1981	81.778
1982	82.226
1983	82.359
1984	82.492
1985	82.624
1986	82.755
1987	82.885
1988	83.014
1989	83.143
1990	83.271
1991	83.398
1992	83.564
1993	83.896
1994	84.223
1995	84.545
1996	84.861
1997	85.172
1998	85.477
1999	85.778
2000	86.073
2001	86.363
2002	86.606
2003	86.665
2004	86.725
2005	86.783
2006	86.842
2007	86.9
2008	86.959
2009	87.017
2010	87.074
2011	87.132
2012	87.189
2013	87.246
2014	87.303
2015	87.36
2016	87.422
2017	87.49