Year	Percent
1960	3.51886
1961	3.72891
1962	3.89859
1963	3.97781
1964	3.94965
1965	3.86441
1966	3.75599
1967	3.70027
1968	3.74995
1969	3.92845
1970	4.17619
1971	4.42058
1972	4.60011
1973	4.70817
1974	4.73213
1975	4.69847
1976	4.64734
1977	4.59932
1978	4.54533
1979	4.48994
1980	4.43007
1981	4.36899
1982	4.29708
1983	4.20318
1984	4.08519
1985	3.95593
1986	3.81673
1987	3.6916
1988	3.6059
1989	3.56805
1990	3.55545
1991	3.54155
1992	3.50216
1993	3.43285
1994	3.3272
1995	3.19481
1996	3.07736
1997	2.96157
1998	2.79979
1999	2.58323
2000	2.34243
2001	2.09688
2002	1.89716
2003	1.78535
2004	1.78485
2005	1.86368
2006	1.96104
2007	2.04587
2008	2.13592
2009	2.22343
2010	2.30546
2011	2.39246
2012	2.47351
2013	2.52502
2014	2.53977
2015	2.52916
2016	2.51035
2017	2.49574