Year	Percent
1960	82.32
1961	82.337
1962	82.355
1963	82.372
1964	82.389
1965	82.5
1966	82.761
1967	83.019
1968	83.275
1969	83.526
1970	83.775
1971	84.021
1972	84.265
1973	84.504
1974	84.741
1975	84.975
1976	85.206
1977	85.434
1978	85.659
1979	85.882
1980	86.101
1981	86.317
1982	86.531
1983	86.742
1984	86.95
1985	87.155
1986	87.357
1987	87.557
1988	87.754
1989	87.949
1990	88.14
1991	88.329
1992	88.398
1993	88.395
1994	88.392
1995	88.388
1996	88.385
1997	88.382
1998	88.379
1999	88.376
2000	88.372
2001	88.369
2002	88.373
2003	88.383
2004	88.399
2005	88.422
2006	88.452
2007	88.488
2008	88.53
2009	88.579
2010	88.634
2011	88.695
2012	88.762
2013	88.835
2014	88.915
2015	88.999
2016	89.09
2017	89.186