Year	Percent
1960	6.66237
1961	5.48675
1962	5.44397
1963	5.31551
1964	5.10667
1965	4.83786
1966	4.54766
1967	4.30606
1968	4.20894
1969	4.29861
1970	4.03854
1971	3.38665
1972	3.6066
1973	3.63102
1974	3.41889
1975	3.0722
1976	2.66754
1977	2.37736
1978	2.32794
1979	2.60448
1980	3.07808
1981	3.59902
1982	3.99568
1983	4.20026
1984	4.5837
1985	5.3478
1986	5.09683
1987	4.90545
1988	4.7799
1989	4.72555
1990	4.73425
1991	4.75332
1992	4.74054
1993	4.68978
1994	4.60404
1995	4.48696
1996	4.37083
1997	4.26924
1998	4.2173
1999	4.206
2000	4.17555
2001	4.03569
2002	4.05638
2003	4.06949
2004	4.07241
2005	4.05592
2006	4.04514
2007	4.02807
2008	3.99365
2009	3.93285
2010	3.86677
2011	3.7908
2012	3.71654
2013	3.64291
2014	3.57641
2015	3.51527
2016	3.45511
2017	3.39287