Year	Percent
1960	2.26355
1961	1.97003
1962	1.68024
1963	1.41558
1964	1.19232
1965	1.00701
1966	0.81711
1967	0.65077
1968	0.59859
1969	0.68261
1970	0.86473
1971	1.09055
1972	1.28566
1973	1.41967
1974	1.46099
1975	1.43758
1976	1.39099
1977	1.36565
1978	1.37116
1979	1.42101
1980	1.49512
1981	1.57673
1982	1.6243
1983	1.59921
1984	1.48357
1985	1.30947
1986	1.1145
1987	0.94112
1988	0.80379
1989	0.72202
1990	0.67961
1991	0.65315
1992	0.61442
1993	0.55764
1994	0.47388
1995	0.37385
1996	0.26761
1997	0.18372
1998	0.14775
1999	0.17671
2000	0.2534
2001	0.34609
2002	0.42796
2003	0.48519
2004	0.50362
2005	0.49462
2006	0.47768
2007	0.46823
2008	0.46574
2009	0.47372
2010	0.48926
2011	0.50231
2012	0.50815
2013	0.4952
2014	0.46212
2015	0.41251
2016	0.35742
2017	0.30453