Year	Percent
1960	2.86042
1961	3.19494
1962	2.83734
1963	2.60892
1964	2.40796
1965	2.23176
1966	2.07825
1967	1.94554
1968	1.83229
1969	1.7373
1970	1.65958
1971	1.589
1972	1.51639
1973	1.48715
1974	1.51742
1975	1.57717
1976	1.61326
1977	1.62727
1978	1.30684
1979	1.74042
1980	1.68601
1981	1.48197
1982	1.22243
1983	0.91967
1984	1.04574
1985	0.81732
1986	0.76452
1987	0.7481
1988	0.6884
1989	0.76591
1990	0.71231
1991	1.07946
1992	1.31574
1993	1.18554
1994	1.40006
1995	0.85993
1996	1.02276
1997	1.2521
1998	1.05142
1999	1.27125
2000	0.98268
2001	0.79005
2002	0.69424
2003	0.72366
2004	0.6271
2005	0.5921
2006	0.4664
2007	0.45553
2008	0.36163
2009	0.26554
2010	0.23789
2011	0.16014
2012	0.27732
2013	0.2204
2014	0.18106
2015	0.13243
2016	0.06872
2017	0.09019