Year	Percent
1960	3.34339
1961	3.44051
1962	3.4806
1963	3.41168
1964	3.21279
1965	2.93853
1966	2.64659
1967	2.40388
1968	2.22525
1969	2.13503
1970	2.11057
1971	2.10476
1972	2.08735
1973	2.05911
1974	2.01544
1975	1.96279
1976	1.87702
1977	1.81135
1978	1.83608
1979	1.98124
1980	2.18294
1981	2.4414
1982	2.6144
1983	2.54049
1984	2.16136
1985	1.59986
1986	0.96308
1987	0.44117
1988	0.16502
1989	0.23585
1990	0.55104
1991	0.93505
1992	1.22407
1993	1.39977
1994	1.39952
1995	1.27581
1996	1.15106
1997	1.06307
1998	0.93587
1999	0.76911
2000	0.58465
2001	0.36852
2002	0.18075
2003	0.11481
2004	0.21113
2005	0.42227
2006	0.67838
2007	0.8905
2008	1.01636
2009	1.01776
2010	0.93265
2011	0.82639
2012	0.74799
2013	0.698
2014	0.69
2015	0.71352
2016	0.73829
2017	0.74735