Year	Percent
1960	4.93092
1961	5.65059
1962	6.24827
1963	6.59679
1964	6.68321
1965	6.63477
1966	6.6484
1967	6.71289
1968	6.67137
1969	6.49447
1970	6.31586
1971	5.90572
1972	5.65389
1973	6.13727
1974	7.38834
1975	8.85702
1976	10.32055
1977	11.00771
1978	10.43805
1979	8.72383
1980	6.58469
1981	4.35471
1982	2.7189
1983	2.19013
1984	3.05468
1985	4.71355
1986	6.53616
1987	7.61866
1988	7.59079
1989	6.38265
1990	4.59838
1991	2.74749
1992	1.34383
1993	0.5579
1994	0.62392
1995	1.28072
1996	2.08693
1997	2.64779
1998	2.93097
1999	2.82294
2000	2.46683
2001	2.08613
2002	1.82704
2003	1.64726
2004	1.58723
2005	1.60904
2006	1.64034
2007	1.64352
2008	1.65803
2009	1.67569
2010	1.69508
2011	1.72285
2012	1.74554
2013	1.74404
2014	1.71118
2015	1.65803
2016	1.59586
2017	1.5429