Year	Percent
1960	25.14992
1961	25.18178
1962	24.42901
1963	19.24204
1964	26.61177
1965	31.8565
1966	34.21859
1967	34.14664
1968	41.40166
1969	40.15458
1970	40.6364
1971	34.8056
1972	40.10563
1973	35.07306
1974	31.02929
1975	41.39515
1976	48.09034
1977	48.42888
1978	39.12512
1979	25.00817
1980	47.86489
1981	40.07582
1982	26.77319
1983	36.26825
1984	33.04527
1985	24.27499
1986	22.21312
1987	20.09298
1988	17.13394
1989	23.04794
1990	33.02184
1991	42.17458
1992	42.19989
1993	30.39529
1994	23.29459
1995	30.18017
1996	37.78609
1997	35.54284
1998	33.85893
1999	32.54167
2000	35.10053
2001	35.25182
2002	39.05411
2003	42.10527
2004	45.99879
2005	38.71766
2006	38.64912
2007	39.72895
2008	41.75745
2009	40.89817
2010	40.26245
2011	36.8811
2012	40.34027
2013	38.69143
2014	39.9059
2015	34.03361
2016	33.20363
2017	34.24676