Year	Percent
1960	0.13706
1961	0.20524
1962	0.2636
1963	0.32618
1964	0.3438
1965	0.37287
1966	0.36453
1967	0.36551
1968	0.35038
1969	0.33769
1970	0.30455
1971	0.20556
1972	-0.17356
1973	-0.25632
1974	-0.39721
1975	-0.58838
1976	-0.79226
1977	-0.95625
1978	-1.02733
1979	-0.96349
1980	-0.79593
1981	-0.33716
1982	0.70939
1983	0.84324
1984	0.92156
1985	0.95776
1986	0.9975
1987	0.75953
1988	0.73777
1989	0.63457
1990	0.47896
1991	0.22168
1992	-0.11078
1993	-0.20379
1994	-0.20648
1995	-0.13865
1996	0.14092
1997	0.66328
1998	0.70597
1999	0.74551
2000	0.75323
2001	0.8133
2002	0.94129
2003	0.95399
2004	0.94285
2005	0.93404
2006	0.92122
2007	0.90867
2008	0.87997
2009	0.84992
2010	0.81451
2011	0.69177
2012	0.43193
2013	0.40623
2014	0.38083
2015	0.37741
2016	0.37403
2017	0.4157