Year	Percent
1960	4.55623
1961	4.14916
1962	3.54204
1963	3.59125
1964	3.63783
1965	3.66707
1966	3.70395
1967	3.73055
1968	3.75277
1969	3.76574
1970	3.77508
1971	3.78112
1972	3.79541
1973	4.01395
1974	4.12466
1975	4.19617
1976	4.2699
1977	4.32631
1978	4.389
1979	4.45018
1980	4.51385
1981	4.42444
1982	4.18835
1983	4.19552
1984	4.17539
1985	4.12815
1986	4.07661
1987	4.0198
1988	3.94476
1989	3.84006
1990	3.72945
1991	3.60907
1992	3.49888
1993	3.41295
1994	3.35815
1995	3.32352
1996	3.30071
1997	3.26395
1998	3.15321
1999	2.96139
2000	2.88157
2001	2.79632
2002	2.7339
2003	2.68343
2004	2.65855
2005	2.64745
2006	2.64052
2007	2.63293
2008	2.63303
2009	2.64452
2010	2.66437
2011	2.68661
2012	2.70076
2013	2.69128
2014	2.66457
2015	2.62165
2016	2.57426
2017	2.52649