Year	Percent
1960	5.48329
1961	5.54248
1962	5.57941
1963	5.53336
1964	5.40377
1965	5.20615
1966	5.01131
1967	4.84473
1968	4.71348
1969	4.62415
1970	4.57718
1971	4.77601
1972	4.74157
1973	4.70759
1974	4.71153
1975	4.728
1976	4.76559
1977	4.7855
1978	4.77596
1979	4.71524
1980	4.60938
1981	4.20241
1982	4.13084
1983	4.13023
1984	4.21634
1985	4.34679
1986	4.50076
1987	4.60343
1988	4.63
1989	4.54619
1990	4.40736
1991	4.24458
1992	4.99301
1993	4.97339
1994	4.89749
1995	4.84971
1996	4.81649
1997	4.74679
1998	4.64882
1999	4.49769
2000	4.32224
2001	3.70297
2002	3.56093
2003	3.44086
2004	3.34809
2005	3.27005
2006	3.19547
2007	3.11914
2008	3.0634
2009	3.02727
2010	3.00696
2011	2.82085
2012	2.77797
2013	2.72388
2014	2.62282
2015	2.48543
2016	2.34064
2017	2.19927