Year	Percent
1960	2.24031
1961	2.38048
1962	2.4992
1963	2.54689
1964	2.50806
1965	2.4097
1966	2.28656
1967	2.1823
1968	2.10734
1969	2.07568
1970	2.06611
1971	2.93228
1972	3.07844
1973	2.96509
1974	2.79067
1975	2.56753
1976	2.34373
1977	2.14141
1978	1.96696
1979	1.8217
1980	1.71249
1981	1.58818
1982	1.22956
1983	1.14679
1984	1.22753
1985	1.36342
1986	1.53865
1987	1.6781
1988	1.7401
1989	1.68595
1990	1.55818
1991	1.19163
1992	0.85697
1993	0.76757
1994	0.72417
1995	0.71196
1996	0.70315
1997	0.73975
1998	0.77109
1999	0.72618
2000	0.6771
2001	0.62813
2002	0.58475
2003	0.45292
2004	0.31965
2005	0.27576
2006	0.2282
2007	0.18789
2008	0.17543
2009	0.19853
2010	0.24776
2011	0.31045
2012	0.36176
2013	0.3233
2014	0.28579
2015	0.23474
2016	0.17107
2017	0.13645