Year	Percent
1960	2.70766
1961	2.71838
1962	2.72877
1963	2.74005
1964	2.75626
1965	2.76545
1966	2.78256
1967	2.79618
1968	2.81026
1969	2.82245
1970	2.83948
1971	2.8488
1972	2.86
1973	2.87228
1974	2.89123
1975	2.91416
1976	2.93098
1977	4.15484
1978	4.52365
1979	4.47421
1980	4.42126
1981	4.35311
1982	4.29764
1983	4.22931
1984	4.16229
1985	4.07983
1986	4.00475
1987	3.93001
1988	3.87272
1989	3.8209
1990	3.78855
1991	3.75496
1992	3.65695
1993	2.9038
1994	2.89296
1995	2.88193
1996	2.86781
1997	2.85248
1998	2.82655
1999	2.79123
2000	2.74815
2001	2.69996
2002	2.59331
2003	2.53682
2004	2.49924
2005	2.46076
2006	2.42699
2007	2.38885
2008	2.35753
2009	2.3244
2010	2.29481
2011	2.26747
2012	2.23884
2013	2.13151
2014	2.05737
2015	2.03441
2016	2.01322
2017	1.98879