Year	Percent
1960	2.94282
1961	2.96671
1962	2.98308
1963	2.98646
1964	2.97847
1965	2.96058
1966	2.93662
1967	2.91147
1968	2.88927
1969	2.87344
1970	2.85888
1971	2.84316
1972	2.82073
1973	2.78587
1974	2.73597
1975	2.67657
1976	2.6155
1977	2.55912
1978	2.50523
1979	2.45689
1980	2.4139
1981	2.37171
1982	2.33084
1983	2.29264
1984	2.25853
1985	2.22654
1986	2.19704
1987	2.16965
1988	2.14587
1989	2.12505
1990	2.10694
1991	2.08938
1992	2.07244
1993	2.06037
1994	2.05279
1995	2.0483
1996	2.04535
1997	2.0388
1998	2.02519
1999	2.00121
2000	1.97122
2001	1.93917
2002	1.91003
2003	1.88445
2004	1.8636
2005	1.84623
2006	1.82798
2007	1.80854
2008	1.79231
2009	1.77908
2010	1.76775
2011	1.75654
2012	1.74202
2013	1.72178
2014	1.69263
2015	1.65788
2016	1.6211
2017	1.58543