Year	Percent
1965	29.63856
1966	28.08336
1967	25.41316
1968	25.37788
1969	25.91563
1970	31.8009
1971	31.92103
1972	29.39416
1973	30.87439
1974	37.00206
1975	36.14199
1976	29.20615
1977	27.96713
1978	24.37865
1979	27.75554
1980	31.22439
1981	28.37717
1982	28.65448
1983	28.37204
1984	27.20849
1985	26.92631
1986	26.03602
1987	26.7878
1988	29.09034
1989	31.98338
1990	30.11867
1991	24.07258
1992	21.05195
1993	18.57303
1994	19.75366
1995	20.34275
1996	20.24299
1997	21.76669
1998	23.03085
1999	22.40177
2000	23.89385
2001	23.20527
2002	22.07851
2003	22.25059
2004	22.90869
2005	24.64672
2006	24.02181
2007	25.50004
2008	25.10131
2009	21.22754
2010	21.63495
2011	23.50903
2012	22.52682
2013	21.41754
2014	20.9462
2015	20.92183
2016	21.89755
2017	22.80491