Year	Percent
1960	73.687
1961	74.417
1962	75.093
1963	75.757
1964	76.409
1965	77.048
1966	77.619
1967	78.163
1968	78.698
1969	79.222
1970	79.737
1971	80.239
1972	80.731
1973	81.211
1974	81.683
1975	82.146
1976	82.6
1977	82.886
1978	83.169
1979	83.448
1980	83.723
1981	83.915
1982	84.025
1983	84.134
1984	84.243
1985	84.351
1986	84.458
1987	84.565
1988	84.671
1989	84.777
1990	84.843
1991	84.871
1992	84.898
1993	84.925
1994	84.952
1995	84.979
1996	85.006
1997	85.033
1998	85.06
1999	85.086
2000	85.1
2001	85.15
2002	85.25
2003	85.36
2004	85.566
2005	85.856
2006	86.098
2007	86.293
2008	86.487
2009	86.654
2010	86.795
2011	86.957
2012	87.142
2013	87.292
2014	87.41
2015	87.526
2016	87.642
2017	87.757