Year	Percent
1960	6.13408
1961	6.05245
1962	5.97992
1963	5.89242
1964	5.80856
1965	4.49361
1966	4.41231
1967	4.36483
1968	4.27871
1969	4.13351
1970	3.96637
1971	3.7902
1972	3.6412
1973	3.53078
1974	3.43871
1975	3.40817
1976	3.41133
1977	3.39592
1978	3.38438
1979	3.36796
1980	3.34459
1981	3.32006
1982	3.29605
1983	3.25717
1984	3.19872
1985	3.12635
1986	2.89036
1987	2.76098
1988	2.69893
1989	2.6409
1990	2.58936
1991	2.53642
1992	2.48571
1993	2.42386
1994	2.35969
1995	2.29304
1996	2.22778
1997	2.16122
1998	2.10997
1999	2.06984
2000	2.03669
2001	2.00636
2002	1.97413
2003	1.93668
2004	1.89022
2005	1.83844
2006	1.78629
2007	1.73468
2008	1.68439
2009	1.63449
2010	1.58382
2011	1.53307
2012	1.48413
2013	1.43598
2014	1.39054
2015	1.34828
2016	1.30713
2017	1.26468