Year	Percent
1960	46.23942
1961	45.24516
1962	45.23589
1963	40.83065
1964	38.26156
1965	38.04408
1966	39.775
1967	38.84116
1968	28.74356
1969	27.77965
1970	17.13131
1971	19.7833
1972	16.79259
1973	22.49451
1974	28.57848
1975	27.27403
1976	24.23564
1977	21.23941
1978	21.41549
1979	23.96637
1980	30.34009
1981	34.77179
1982	35.09903
1983	26.52591
1984	23.44461
1985	20.9249
1986	22.41773
1987	22.50344
1988	26.43178
1989	18.89705
1990	15.34104
1991	17.63618
1992	17.62739
1993	19.49363
1994	22.24713
1995	24.73911
1996	22.58676
1997	23.78942
1998	23.20495
1999	20.66125
2000	19.62798
2001	18.15951
2002	17.96815
2003	17.51029
2004	16.85568
2005	17.28382
2006	19.6506
2007	22.03239
2008	26.17835
2009	19.97868
2010	23.76051
2011	24.20088
2012	24.60606
2013	25.56477
2014	24.62286
2015	24.24314
2016	22.10256
2017	20.93164