Year	Percent
1960	1.43887
1961	1.34621
1962	0.7202
1963	0.32241
1964	0.17867
1965	0.0357
1966	-0.0714
1967	-0.03572
1968	0.14281
1969	0.88795
1970	1.78733
1971	2.90967
1972	3.57891
1973	4.14468
1974	4.27938
1975	3.9025
1976	3.36713
1977	3.12269
1978	3.13272
1979	3.64423
1980	4.60502
1981	8.13193
1982	8.36035
1983	8.4116
1984	8.00138
1985	7.45656
1986	6.66862
1987	6.19506
1988	5.99343
1989	6.43139
1990	6.95503
1991	7.10092
1992	7.57954
1993	7.57799
1994	7.07002
1995	6.22835
1996	5.29199
1997	4.6425
1998	4.61304
1999	5.34358
2000	6.50525
2001	7.67544
2002	8.18715
2003	8.08651
2004	7.34842
2005	6.15811
2006	5.02521
2007	4.12628
2008	3.45502
2009	3.08948
2010	2.95399
2011	2.83794
2012	2.6446
2013	2.49725
2014	2.2913
2015	2.13579
2016	1.96732
2017	1.8777