Year	Percent
1960	0.67351
1961	0.65178
1962	0.68966
1963	0.71869
1964	0.67751
1965	0.59127
1966	0.57638
1967	0.54522
1968	0.54851
1969	0.60016
1970	0.49741
1971	0.48766
1972	0.53657
1973	0.54422
1974	0.56574
1975	0.57358
1976	0.5981
1977	0.53426
1978	0.50483
1979	0.5053
1980	0.41611
1981	0.5133
1982	0.49542
1983	0.52287
1984	0.65982
1985	0.67631
1986	0.63462
1987	0.58034
1988	0.53615
1989	0.51726
1990	0.50521
1991	0.50867
1992	0.55006
1993	0.57722
1994	0.68655
1995	0.59858
1996	0.62105
1997	0.59724
1998	0.58929
1999	0.60511
2000	0.57217
2001	0.56929
2002	0.53644
2003	0.45496
2004	0.40636
2005	0.41877
2006	0.42293
2007	0.45822
2008	0.44854
2009	0.54255
2010	0.56103
2011	0.55255
2012	0.58813
2013	0.62106
2014	0.6672
2015	0.67168
2016	0.57525
2017	0.50174