Year	Percent
1964	37.40247
1965	39.73928
1966	39.993
1967	41.315
1968	40.49968
1969	40.3616
1970	41.54334
1971	40.52499
1972	42.86709
1973	38.28332
1974	38.96196
1975	45.15079
1976	39.51059
1977	32.65669
1978	29.42857
1979	29.9979
1980	28.13187
1981	33.00383
1982	31.57738
1983	30.38474
1984	28.45929
1985	27.72317
1986	27.77948
1987	23.25247
1988	23.86593
1989	23.68053
1990	16.80541
1991	16.75287
1992	15.61521
1993	15.08728
1994	14.06959
1995	5.26706
1996	1.88206
1997	10.23995
1998	7.09121
1999	7.19783
2000	4.2467
2001	4.18545
2002	3.24287
2003	4.148
2004	7.72608
2005	7.21796
2006	7.70299
2007	7.92877
2008	7.09469
2009	5.00972
2010	5
2011	8.30008
2012	16.39666
2013	15.75787
2014	15.70935
2015	12.53687
2016	13.002
2017	12.18721