Year	Percent
1960	11.27435
1961	11.32886
1962	11.38024
1963	11.4256
1964	11.46278
1965	11.48963
1966	11.5067
1967	11.5181
1968	11.53608
1969	11.57256
1970	11.58329
1971	11.55967
1972	11.56046
1973	11.57484
1974	11.59203
1975	11.60369
1976	11.60851
1977	11.60841
1978	11.60808
1979	11.54302
1980	11.40493
1981	11.27532
1982	11.15311
1983	11.03638
1984	10.92322
1985	10.81175
1986	10.70309
1987	10.59793
1988	10.49653
1989	10.38551
1990	10.24068
1991	10.08804
1992	9.85756
1993	9.63926
1994	9.455
1995	9.28877
1996	9.11581
1997	8.95806
1998	8.8369
1999	8.76385
2000	8.6595
2001	8.56105
2002	8.48793
2003	8.42049
2004	8.35446
2005	8.28808
2006	8.21759
2007	8.13115
2008	8.03104
2009	7.98916
2010	7.85789
2011	7.73951
2012	7.71599
2013	7.68538
2014	7.64546
2015	7.60138
2016	7.55809
2017	7.51953