Year	Percent
1960	4.77842
1961	4.80298
1962	4.83859
1963	4.85965
1964	4.87673
1965	4.87711
1966	4.88057
1967	4.88056
1968	4.89993
1969	4.9254
1970	4.97317
1971	5.01787
1972	5.04579
1973	5.03405
1974	5.08039
1975	5.14177
1976	5.05652
1977	4.97089
1978	4.91463
1979	4.88105
1980	4.86383
1981	4.84409
1982	4.81984
1983	4.7736
1984	4.70689
1985	4.11673
1986	3.59636
1987	3.55264
1988	3.51823
1989	3.49922
1990	3.49275
1991	3.48929
1992	3.48693
1993	3.49056
1994	3.50101
1995	3.52237
1996	3.55663
1997	3.66873
1998	3.67277
1999	3.6441
2000	3.60373
2001	3.5366
2002	3.49473
2003	3.52667
2004	3.65393
2005	3.82963
2006	4.02369
2007	4.158
2008	4.16987
2009	4.0303
2010	3.80188
2011	3.55096
2012	3.35279
2013	3.22669
2014	3.19439
2015	3.22596
2016	3.26869
2017	3.28983