Year	Percent
1960	2.62028
1961	2.63682
1962	2.64911
1963	2.66271
1964	2.68044
1965	2.69873
1966	2.71283
1967	2.71825
1968	2.71444
1969	2.70029
1970	2.6782
1971	2.6529
1972	2.62589
1973	2.59514
1974	2.561
1975	2.52455
1976	2.48305
1977	2.44098
1978	2.40579
1979	2.37976
1980	2.3578
1981	2.33768
1982	2.3095
1983	2.2641
1984	2.19736
1985	2.11701
1986	2.03347
1987	1.9563
1988	1.8874
1989	1.83017
1990	1.78146
1991	1.73704
1992	1.69191
1993	1.64455
1994	1.59336
1995	1.54137
1996	1.49017
1997	1.44593
1998	1.41436
1999	1.39844
2000	1.39374
2001	1.39239
2002	1.38959
2003	1.38668
2004	1.38215
2005	1.37595
2006	1.36919
2007	1.36163
2008	1.35146
2009	1.33807
2010	1.3214
2011	1.30407
2012	1.2842
2013	1.25733
2014	1.22205
2015	1.18101
2016	1.13749
2017	1.09538