Year	Percent
1960	4.40151
1961	4.39752
1962	4.40126
1963	4.39393
1964	4.39348
1965	4.36956
1966	4.36817
1967	4.35024
1968	4.31931
1969	4.24772
1970	4.16654
1971	4.07996
1972	2.22328
1973	1.84264
1974	1.87689
1975	1.94648
1976	2.0187
1977	2.08743
1978	2.15433
1979	2.23255
1980	2.31456
1981	2.38794
1982	2.4516
1983	5.99419
1984	6.62189
1985	6.51189
1986	6.40499
1987	6.2946
1988	6.19548
1989	6.08188
1990	5.99389
1991	5.89361
1992	5.79846
1993	3.8245
1994	3.78084
1995	3.7379
1996	3.70111
1997	3.58859
1998	3.54154
1999	3.48969
2000	3.43087
2001	6.19638
2002	6.04373
2003	5.89074
2004	4.08852
2005	3.84404
2006	3.80468
2007	3.75488
2008	3.70638
2009	3.63402
2010	3.5649
2011	3.49193
2012	3.42184
2013	3.34338
2014	3.27094
2015	3.19518
2016	3.09564
2017	2.99033