Year	Percent
1964	26.52674
1965	26.84067
1966	24.94407
1967	26.14806
1968	27.75723
1969	26.24972
1970	25.39996
1971	26.21908
1972	26.94081
1973	24.37261
1974	21.5466
1975	19.53155
1976	19.44039
1977	19.44212
1978	19.42498
1979	19.19279
1980	20.16443
1981	17.87649
1982	15.95513
1983	14.17835
1984	13.11596
1985	12.95879
1986	14.66632
1987	17.92901
1988	11.29917
1989	10.1651
1990	17.96943
1991	33.79119
1992	38.80739
1993	31.11476
1994	38.35755
1995	36.06692
1996	36.30321
1997	27.09431
1998	23.75265
1999	24.30554
2000	26.75921
2001	7.90551
2002	8.80633
2003	10.34227
2004	11.77687
2005	11.25731
2006	10.36752
2007	9.66533
2008	7.83422
2009	6.54721
2010	7.78137
2011	7.86963
2012	14.53438
2013	21.22851
2014	15.61407
2015	4.55593
2016	5.61093
2017	5.13776