Year	Percent
1960	4.24894
1961	4.71362
1962	4.6265
1963	4.52345
1964	4.40279
1965	4.25885
1966	4.13105
1967	4.01062
1968	3.9054
1969	3.81948
1970	3.75168
1971	3.68657
1972	3.98122
1973	3.97084
1974	3.98782
1975	4.02915
1976	4.07623
1977	4.10446
1978	4.13028
1979	4.14389
1980	4.14189
1981	4.13486
1982	4.12214
1983	4.06402
1984	3.97557
1985	3.85434
1986	3.72883
1987	3.60936
1988	3.50995
1989	3.42738
1990	3.36738
1991	3.31222
1992	3.24773
1993	3.15824
1994	3.04967
1995	2.29005
1996	2.04967
1997	1.95001
1998	1.87231
1999	1.82049
2000	1.78424
2001	1.75619
2002	1.73568
2003	1.72107
2004	1.71762
2005	2.09139
2006	2.16603
2007	2.16744
2008	2.18632
2009	2.22631
2010	2.28392
2011	2.34215
2012	2.38822
2013	2.40125
2014	2.37492
2015	2.31761
2016	2.25326
2017	2.19249