Year	Percent
1960	23.27272
1961	26.49007
1962	24.59017
1963	25.23659
1964	28.44827
1965	27.10027
1966	28.35052
1967	26.30273
1968	34.3123
1969	27.33466
1970	31.9385
1971	29.79923
1972	24.9348
1973	28.61804
1974	27.73682
1975	21.13035
1976	22.18687
1977	25.2044
1978	23.42032
1979	22.43257
1980	25.22155
1981	24.38345
1982	22.17775
1983	24.149
1984	23.39399
1985	22.00852
1986	18.18643
1987	17.84414
1988	17.74475
1989	20.30389
1990	17.06747
1991	17.58667
1992	16.8657
1993	17.09955
1994	23.39941
1995	22.22094
1996	21.47039
1997	26.88428
1998	22.65689
1999	19.22365
2000	20.37221
2001	17.15725
2002	15.9627
2003	18.236
2004	13.99792
2005	13.36275
2006	14.31601
2007	14.11533
2008	11.00366
2009	10.68442
2010	11.80725
2011	11.51483
2012	11.64916
2013	14.45149
2014	13.03009
2015	12.61192
2016	12.72904
2017	12.51809