Year	Percent
1960	4.8573
1961	4.24357
1962	4.04843
1963	3.82448
1964	3.57356
1965	3.49846
1966	3.58469
1967	4.34571
1968	4.69018
1969	4.78879
1970	4.1973
1971	4.1192
1972	3.95653
1973	3.51771
1974	4.82447
1975	5.84732
1976	5.82923
1977	5.91854
1978	5.57544
1979	5.18125
1980	4.66081
1981	5.7357
1982	5.62659
1983	5.17248
1984	4.83544
1985	4.69257
1986	4.12802
1987	4.25552
1988	4.19823
1989	3.76587
1990	3.79826
1991	3.48487
1992	3.6298
1993	3.60012
1994	3.58197
1995	3.17319
1996	3.31191
1997	3.36587
1998	3.53387
1999	3.36047
2000	3.46536
2001	3.25141
2002	3.07737
2003	2.49389
2004	2.60567
2005	2.8366
2006	2.78342
2007	2.67931
2008	2.98305
2009	3.22484
2010	2.72701
2011	2.47695
2012	2.40769
2013	2.35768
2014	2.34297
2015	2.47272
2016	2.55174
2017	2.50616