Year	Percent
1960	4.18585
1961	4.1465
1962	2.71819
1963	2.73424
1964	2.79677
1965	2.84482
1966	2.92555
1967	2.97654
1968	3.04756
1969	3.08207
1970	3.13455
1971	3.25935
1972	6.77303
1973	6.7789
1974	6.82009
1975	6.82688
1976	6.86345
1977	6.86756
1978	6.86317
1979	6.88589
1980	6.89684
1981	6.87367
1982	6.01702
1983	6.0053
1984	5.98284
1985	5.93209
1986	5.87287
1987	5.83699
1988	5.85596
1989	5.93383
1990	6.06065
1991	6.22502
1992	6.99615
1993	6.99056
1994	6.90008
1995	6.72745
1996	6.54352
1997	6.37234
1998	6.21666
1999	6.08502
2000	5.96315
2001	5.78057
2002	3.73958
2003	3.62326
2004	3.49065
2005	3.3528
2006	3.2096
2007	3.09373
2008	3.02305
2009	3.01911
2010	3.06116
2011	3.12609
2012	3.19943
2013	3.22995
2014	3.23943
2015	3.21049
2016	3.18634
2017	3.16435