Year	Percent
1960	3.53157
1961	3.76454
1962	3.71108
1963	3.38734
1964	3.42247
1965	3.55442
1966	3.14398
1967	3.25957
1968	3.27556
1969	3.07934
1970	3.25649
1971	3.49979
1972	3.44552
1973	3.34945
1974	3.19302
1975	5.11945
1976	4.94303
1977	4.71362
1978	4.18731
1979	3.35726
1980	3.90031
1981	3.82453
1982	4.29815
1983	3.93761
1984	3.59709
1985	3.53104
1986	3.63799
1987	3.32859
1988	2.93221
1989	3.14873
1990	3.52771
1991	3.75436
1992	3.87057
1993	3.92142
1994	4.05136
1995	3.90165
1996	4.1397
1997	4.10367
1998	3.1845
1999	3.88902
2000	3.66109
2001	3.60346
2002	3.79593
2003	3.29605
2004	2.69798
2005	2.40937
2006	2.41867
2007	2.26697
2008	2.24084
2009	2.53659
2010	2.32413
2011	2.07854
2012	2.05476
2013	1.96325
2014	1.90246
2015	1.84794
2016	2.08192
2017	2.17814