Year	Percent
1960	15.95496
1961	15.8931
1962	15.8145
1963	15.74836
1964	15.68447
1965	15.52875
1966	15.29878
1967	15.09831
1968	14.91466
1969	14.71585
1970	14.53304
1971	14.3861
1972	14.26773
1973	14.17795
1974	14.09661
1975	13.94523
1976	13.75332
1977	13.59016
1978	13.4261
1979	13.25411
1980	13.09287
1981	12.96961
1982	12.87721
1983	12.7961
1984	12.7137
1985	12.67062
1986	12.66433
1987	12.64797
1988	12.63028
1989	12.61826
1990	12.62087
1991	12.63718
1992	12.65779
1993	12.68569
1994	12.72584
1995	12.73865
1996	12.71356
1997	12.68166
1998	12.63703
1999	12.5864
2000	12.53039
2001	12.47009
2002	12.42461
2003	12.39993
2004	12.39075
2005	12.40443
2006	12.43639
2007	12.46149
2008	12.46545
2009	12.45383
2010	12.44262
2011	12.43736
2012	12.44431
2013	12.46063
2014	12.4691
2015	12.46733
2016	12.45463
2017	12.43361