Year	Percent
1960	2.4245
1961	2.50586
1962	2.81143
1963	3.30406
1964	3.14603
1965	2.9192
1966	2.67069
1967	2.44766
1968	1.96797
1969	1.28593
1970	1.34
1971	1.41914
1972	1.46781
1973	1.45564
1974	1.3659
1975	1.06381
1976	0.62844
1977	0.50519
1978	0.43303
1979	0.42882
1980	0.47746
1981	0.53729
1982	0.58923
1983	0.63338
1984	0.66044
1985	0.67561
1986	0.69339
1987	0.71224
1988	0.71534
1989	0.6983
1990	0.709
1991	0.31278
1992	0.72869
1993	0.66286
1994	0.60128
1995	0.5871
1996	0.58076
1997	0.57725
1998	0.59028
1999	0.77533
2000	1.02424
2001	1.06463
2002	1.05902
2003	1.03817
2004	1.06332
2005	1.07455
2006	1.01693
2007	0.93354
2008	0.87656
2009	0.83375
2010	0.8161
2011	0.80596
2012	0.80906
2013	0.84007
2014	0.80657
2015	0.74544
2016	0.72762
2017	0.715