Year	Percent
1960	2.77685
1961	2.86638
1962	2.93265
1963	2.96232
1964	2.95016
1965	2.90872
1966	2.85297
1967	2.79576
1968	2.74132
1969	2.69403
1970	2.64852
1971	2.59832
1972	2.53754
1973	2.46531
1974	2.38128
1975	2.28785
1976	2.19748
1977	2.10726
1978	2.00183
1979	1.87923
1980	1.74829
1981	1.61674
1982	1.49998
1983	1.41164
1984	1.36001
1985	1.33564
1986	1.31313
1987	1.28994
1988	1.28425
1989	1.29858
1990	1.32253
1991	1.35469
1992	1.37364
1993	1.35494
1994	1.28771
1995	1.18628
1996	1.07791
1997	0.97951
1998	0.88561
1999	0.80113
2000	0.7259
2001	0.65122
2002	0.57978
2003	0.52439
2004	0.48846
2005	0.46861
2006	0.45538
2007	0.44476
2008	0.44
2009	0.4405
2010	0.44465
2011	0.45211
2012	0.46216
2013	0.47356
2014	0.48535
2015	0.4969
2016	0.5095
2017	0.52082