Year	Percent
1960	6.03654
1961	6.02516
1962	6.0459
1963	6.08318
1964	6.14556
1965	6.19874
1966	5.60912
1967	5.42211
1968	5.45149
1969	5.40776
1970	5.32379
1971	5.22045
1972	5.12576
1973	5.03648
1974	4.97941
1975	4.927
1976	4.87658
1977	4.80194
1978	4.35879
1979	4.09821
1980	3.96623
1981	3.84438
1982	3.73719
1983	3.61462
1984	3.47864
1985	3.33764
1986	3.19528
1987	3.08652
1988	2.27433
1989	2.04409
1990	2.22317
1991	2.41128
1992	2.56593
1993	2.68863
1994	2.76293
1995	2.80084
1996	2.83367
1997	2.85835
1998	3.09194
1999	3.13189
2000	3.03861
2001	2.94926
2002	2.87477
2003	2.80128
2004	2.73156
2005	2.67342
2006	2.59786
2007	2.54796
2008	2.58619
2009	2.73178
2010	3.04049
2011	3.32517
2012	3.49091
2013	3.55486
2014	3.49434
2015	3.35384
2016	3.21228
2017	3.10307