Year	Percent
1960	19.41666
1961	9.38717
1962	7.44127
1963	31.68264
1964	37.30448
1965	27.23323
1966	38.02089
1967	16.37136
1968	15.30187
1969	14.22881
1970	18.22372
1971	18.53598
1972	15.77741
1973	15.87628
1974	19.03048
1975	15.09093
1976	19.64917
1977	19.67275
1978	9.19737
1979	10.04147
1980	16.35191
1981	17.14198
1982	13.9526
1983	17.29085
1984	26.11731
1985	25.63434
1986	24.03151
1987	28.86172
1988	27.82202
1989	24.83869
1990	29.20457
1991	20
1992	17.51412
1993	9.10104
1994	19.89143
1995	23.72624
1996	30.31349
1997	15
1998	32.88922
1999	17.54199
2000	15.56479
2001	13.05425
2002	13.6455
2003	30.03091
2004	26.6069
2005	29.37042
2006	26.26316
2007	41.07014
2008	44.74449
2009	36.13309
2010	49.63646
2011	45.68253
2012	37.5487
2013	41.02008
2014	41.85796
2015	31.60686
2016	32.37186
2017	39.43164