Year	Percent
1960	27.93075
1961	28.73927
1962	30.45042
1963	32.60034
1964	29.25149
1965	23.97856
1966	24.7025
1967	22.8581
1968	25.19528
1969	23.51402
1970	24.03585
1971	24.84507
1972	23.50045
1973	24.36529
1974	21.60091
1975	23.67095
1976	21.99034
1977	20.01695
1978	22.3175
1979	18.19798
1980	28.39206
1981	22.05361
1982	19.26407
1983	24.02142
1984	18.29641
1985	9.22303
1986	8.20594
1987	6.81698
1988	10.19536
1989	13.11839
1990	7.99442
1991	10.5016
1992	16.19227
1993	15.32349
1994	13.52176
1995	12.82019
1996	24.02907
1997	18.61063
1998	22.40824
1999	20.5485
2000	27.41197
2001	27.74031
2002	29.68955
2003	30.73697
2004	36.59798
2005	43.6607
2006	38.33076
2007	38.4633
2008	38.55379
2009	33.76826
2010	32.6793
2011	28.85797
2012	19.51808
2013	20.40881
2014	16.63388
2015	13.04923
2016	11.94446
2017	7.78056