Year	Percent
1960	7.83501
1961	8.01243
1962	8.15297
1963	8.29422
1964	8.43265
1965	8.56417
1966	8.66904
1967	8.70404
1968	8.7361
1969	8.76844
1970	8.80498
1971	8.8459
1972	8.89009
1973	8.93443
1974	8.97747
1975	9.01699
1976	9.05392
1977	8.99726
1978	8.79351
1979	8.58939
1980	8.38487
1981	8.18046
1982	7.97835
1983	7.78105
1984	7.59136
1985	7.41089
1986	7.24017
1987	7.10399
1988	7.03987
1989	6.98326
1990	6.93518
1991	6.89513
1992	6.86333
1993	6.84028
1994	6.82773
1995	6.82602
1996	6.835
1997	6.85293
1998	6.87828
1999	6.86931
2000	6.86442
2001	6.8626
2002	6.86324
2003	6.8638
2004	6.86157
2005	6.85413
2006	6.84159
2007	6.82401
2008	6.80065
2009	6.77039
2010	6.73362
2011	6.69012
2012	6.64146
2013	6.59121
2014	6.54367
2015	6.50171
2016	6.46612
2017	6.43633