Year	Percent
1960	3.01266
1961	3.08565
1962	3.14476
1963	3.17556
1964	3.17166
1965	3.14905
1966	3.11595
1967	3.09872
1968	3.12067
1969	3.19076
1970	3.28795
1971	3.38764
1972	3.46309
1973	3.50628
1974	3.50947
1975	3.48569
1976	3.44851
1977	3.41636
1978	3.39829
1979	3.40068
1980	3.41077
1981	3.42132
1982	3.41169
1983	3.36554
1984	3.27658
1985	3.16146
1986	3.05058
1987	2.95467
1988	2.86139
1989	2.77347
1990	2.695
1991	2.61254
1992	2.54678
1993	2.53372
1994	2.58412
1995	2.67265
1996	2.7763
1997	2.85708
1998	2.89207
1999	2.86786
2000	2.80706
2001	2.74332
2002	2.70046
2003	2.67579
2004	2.67586
2005	2.69451
2006	2.7117
2007	2.72845
2008	2.76317
2009	2.81793
2010	2.88315
2011	2.95043
2012	3.00513
2013	3.03692
2014	3.04021
2015	3.02412
2016	3.00282
2017	2.98512