Year	Percent
1960	4.31233
1961	4.42025
1962	4.50297
1963	4.48834
1964	4.46728
1965	4.42733
1966	4.38685
1967	4.34738
1968	4.30713
1969	4.27133
1970	4.1306
1971	3.42709
1972	3.40337
1973	3.36511
1974	3.31193
1975	3.24712
1976	3.18688
1977	3.12323
1978	3.07013
1979	3.01667
1980	2.98645
1981	3.04144
1982	2.99808
1983	2.95357
1984	2.91696
1985	2.87689
1986	2.84508
1987	2.81162
1988	2.78565
1989	2.75883
1990	2.863
1991	3.66127
1992	3.61645
1993	3.57202
1994	3.53845
1995	3.50355
1996	3.47473
1997	3.43458
1998	3.39525
1999	3.34291
2000	3.1795
2001	2.41876
2002	2.38409
2003	2.35633
2004	2.33167
2005	2.31056
2006	2.28856
2007	2.26394
2008	2.24563
2009	2.2288
2010	2.2124
2011	2.21142
2012	2.20551
2013	2.19374
2014	2.17444
2015	2.14633
2016	2.11617
2017	2.08843