Year	Percent
1960	0.78067
1961	0.70571
1962	0.68
1963	0.70698
1964	0.55632
1965	0.33337
1966	0.3748
1967	0.54155
1968	0.44897
1969	-0.05803
1970	-0.37872
1971	0.1262
1972	0.5952
1973	0.56791
1974	0.52354
1975	0.44386
1976	0.30145
1977	0.27974
1978	0.28712
1979	0.25558
1980	0.31108
1981	0.42652
1982	0.56029
1983	0.59599
1984	0.53434
1985	0.41707
1986	0.32479
1987	0.28363
1988	0.29069
1989	0.36102
1990	0.44338
1991	0.54617
1992	0.56191
1993	0.48385
1994	0.43105
1995	0.38166
1996	0.32804
1997	0.29738
1998	0.26547
1999	0.23212
2000	0.20761
2001	0.22769
2002	0.24238
2003	0.23846
2004	0.29035
2005	0.34225
2006	0.38378
2007	0.42543
2008	0.46555
2009	0.47825
2010	0.45749
2011	0.46356
2012	0.47581
2013	0.46072
2014	0.41356
2015	0.32938
2016	0.28742
2017	0.29073