Year	Percent
1964	33.57211
1965	36.22906
1966	35.90604
1967	40.26128
1968	41.76318
1969	37.42201
1970	36.40798
1971	39.27125
1972	40.89422
1973	38.08685
1974	37.54208
1975	38.62345
1976	41.72811
1977	41.89135
1978	40.00811
1979	41.00801
1980	41.41064
1981	43.58458
1982	44.15706
1983	45.15218
1984	44.45869
1985	39.03098
1986	42.04379
1987	33.97075
1988	39.54709
1989	39.73632
1990	31.79985
1991	24.1096
1992	19.92208
1993	22.19867
1994	19.19459
1995	17.13055
1996	13.73681
1997	13.37333
1998	12.96228
1999	12.43525
2000	12.49023
2001	41.4624
2002	40.17713
2003	38.78148
2004	35.99161
2005	36.23474
2006	35.58215
2007	34.72307
2008	35.09655
2009	34.59809
2010	35.26109
2011	35.25357
2012	32.55502
2013	28.47955
2014	29.82684
2015	33.87134
2016	33.28609
2017	32.38898