Year	Percent
1960	0.83937
1961	0.79435
1962	0.8034
1963	0.75612
1964	0.7554
1965	0.77733
1966	0.79838
1967	0.83654
1968	0.8406
1969	0.81473
1970	0.72652
1971	0.70129
1972	0.7648
1973	0.6995
1974	0.62035
1975	0.55189
1976	0.46901
1977	0.42266
1978	0.38179
1979	0.34057
1980	0.32123
1981	0.34408
1982	0.36728
1983	0.33106
1984	0.2822
1985	0.29947
1986	0.35669
1987	0.46805
1988	0.53792
1989	0.41281
1990	0.34415
1991	0.4765
1992	0.57718
1993	0.59523
1994	0.56939
1995	0.51913
1996	0.50688
1997	0.54222
1998	0.59541
1999	0.68476
2000	0.64904
2001	0.50605
2002	0.53929
2003	0.58653
2004	0.59093
2005	0.68107
2006	0.80539
2007	1.03473
2008	1.24633
2009	1.26113
2010	1.24567
2011	1.29719
2012	1.31344
2013	1.20914
2014	1.12774
2015	1.02653
2016	0.84952
2017	0.90721