Year	Percent
1960	2.75589
1961	2.73368
1962	2.70755
1963	2.68266
1964	2.66173
1965	2.64134
1966	2.62635
1967	2.60449
1968	2.55885
1969	2.48427
1970	2.39518
1971	2.30475
1972	2.23415
1973	2.19644
1974	2.2002
1975	2.23383
1976	2.27398
1977	2.31149
1978	2.35628
1979	2.40663
1980	2.45935
1981	2.50219
1982	2.53979
1983	2.58582
1984	2.64239
1985	2.69721
1986	2.75566
1987	2.78698
1988	2.75274
1989	2.64009
1990	2.4788
1991	2.30747
1992	2.16048
1993	2.04451
1994	1.97167
1995	1.93119
1996	1.89526
1997	1.85788
1998	1.83776
1999	1.83618
2000	1.84702
2001	1.87198
2002	1.89577
2003	1.89922
2004	1.87461
2005	1.83529
2006	1.78257
2007	1.74797
2008	1.76541
2009	1.84946
2010	1.97228
2011	2.10584
2012	2.2057
2013	2.24553
2014	2.20814
2015	2.11829
2016	2.01679
2017	1.92974