Year	Percent
1960	3.79408
1961	3.81951
1962	3.81927
1963	4.14585
1964	5.17067
1965	5.03722
1966	4.91298
1967	4.79187
1968	4.66151
1969	4.51427
1970	4.369
1971	4.22094
1972	4.09946
1973	3.92457
1974	3.31647
1975	3.34477
1976	3.38665
1977	3.411
1978	3.44117
1979	3.4613
1980	3.47532
1981	3.4878
1982	3.50417
1983	3.49348
1984	3.53174
1985	4.62128
1986	4.5368
1987	4.45737
1988	4.40088
1989	4.37059
1990	4.36463
1991	4.35167
1992	4.32487
1993	4.27451
1994	4.21375
1995	4.13589
1996	4.06147
1997	3.97233
1998	3.85128
1999	3.68379
2000	3.50101
2001	4.07505
2002	3.84659
2003	3.65911
2004	3.52155
2005	3.41626
2006	3.32965
2007	3.23249
2008	3.13266
2009	3.01105
2010	2.89402
2011	2.77268
2012	2.62796
2013	2.49232
2014	2.36832
2015	2.25672
2016	2.1521
2017	2.04915