Year	Percent
1964	29.51622
1965	31.28165
1966	31.6182
1967	31.31433
1968	26.84776
1969	25.19269
1970	29.28108
1971	32.38659
1972	29.03382
1973	23.40366
1974	26.13347
1975	34.47127
1976	28.92646
1977	26.72977
1978	24.00785
1979	27.08567
1980	38.21722
1981	39.73843
1982	25.93331
1983	22.03507
1984	12.4052
1985	16.60939
1986	15.01014
1987	23.18886
1988	14.39149
1989	17.67078
1990	34.00077
1991	28.99467
1992	32.90193
1993	28.57729
1994	25.64852
1995	26.44081
1996	32.1503
1997	15.07833
1998	21.27112
1999	19.92127
2000	39.39512
2001	27.58445
2002	29.83638
2003	31.98467
2004	29.11737
2005	29.29978
2006	25.04741
2007	24.69181
2008	25.69428
2009	27.93676
2010	34.48259
2011	64.45025
2012	60.36879
2013	58.82604
2014	52.42576
2015	47.44007
2016	54.50191