Year	Percent
1960	3.75056
1961	3.79173
1962	3.81334
1963	3.79222
1964	3.7185
1965	3.61099
1966	3.50487
1967	3.4096
1968	3.30661
1969	3.1968
1970	3.08718
1971	2.97608
1972	2.87859
1973	2.81304
1974	2.78631
1975	2.78494
1976	2.79098
1977	2.78947
1978	2.77918
1979	2.75537
1980	2.723
1981	2.68702
1982	2.65509
1983	2.6307
1984	2.61596
1985	2.60546
1986	2.59618
1987	2.57795
1988	2.54219
1989	2.48475
1990	2.41342
1991	2.33937
1992	2.27086
1993	2.20808
1994	2.15366
1995	2.10558
1996	2.05827
1997	2.01088
1998	1.96784
1999	1.92969
2000	1.89486
2001	1.86157
2002	1.82789
2003	1.79353
2004	1.75767
2005	1.72071
2006	1.68452
2007	1.64864
2008	1.61102
2009	1.57109
2010	1.52987
2011	1.48831
2012	1.44819
2013	1.41096
2014	1.37754
2015	1.34671
2016	1.31706
2017	1.28693