Year	Percent
1960	78.444
1961	78.374
1962	78.237
1963	78.099
1964	77.96
1965	77.821
1966	77.682
1967	77.541
1968	77.4
1969	77.259
1970	77.117
1971	77.03
1972	77.195
1973	77.358
1974	77.521
1975	77.683
1976	77.844
1977	78.005
1978	78.164
1979	78.323
1980	78.481
1981	78.588
1982	78.539
1983	78.489
1984	78.44
1985	78.39
1986	78.34
1987	78.29
1988	78.24
1989	78.19
1990	78.14
1991	78.112
1992	78.172
1993	78.232
1994	78.293
1995	78.353
1996	78.413
1997	78.472
1998	78.532
1999	78.591
2000	78.651
2001	78.751
2002	79.047
2003	79.339
2004	79.629
2005	79.915
2006	80.199
2007	80.479
2008	80.757
2009	81.031
2010	81.302
2011	81.57
2012	81.837
2013	82.102
2014	82.365
2015	82.626
2016	82.886
2017	83.143