Year	Percent
1960	8.19377
1961	8.21509
1962	8.21679
1963	6.30801
1964	4.31618
1965	4.25367
1966	4.18052
1967	4.11781
1968	4.0833
1969	4.27305
1970	4.50664
1971	4.52649
1972	4.52676
1973	4.48801
1974	4.41813
1975	4.32288
1976	4.22631
1977	4.13377
1978	4.0687
1979	3.9004
1980	3.74703
1981	3.69441
1982	3.63841
1983	3.63182
1984	3.68509
1985	3.75235
1986	3.85532
1987	3.89476
1988	3.76989
1989	2.9132
1990	1.91583
1991	1.4538
1992	1.06792
1993	0.79333
1994	0.68224
1995	0.68535
1996	0.72374
1997	0.74127
1998	0.76878
1999	0.78834
2000	1.78799
2001	2.81566
2002	2.82353
2003	2.83806
2004	2.85782
2005	2.87517
2006	2.89374
2007	2.91382
2008	2.95997
2009	3.02826
2010	3.12038
2011	2.36976
2012	1.98929
2013	2.0298
2014	1.98847
2015	1.89403
2016	1.78103
2017	1.67779