Year	Percent
1965	17.04546
1966	17.83341
1967	18.55981
1968	18.65736
1969	19.06362
1970	18.66459
1971	18.8134
1972	18.76354
1973	19.19885
1974	18.72427
1975	18.49365
1976	20.10291
1977	20.88259
1978	21.19655
1979	21.52469
1980	21.98693
1981	21.7465
1982	21.23633
1983	20.50419
1984	19.75626
1985	19.66962
1986	20.09047
1987	19.84642
1988	20.1908
1989	20.10505
1990	19.78776
1991	19.57546
1992	20.00923
1993	19.87963
1994	19.68554
1995	19.66159
1996	19.68544
1997	19.97425
1998	19.99437
1999	20.11987
2000	19.79112
2001	26.90701
2002	26.74806
2003	27.01544
2004	27.43193
2005	27.14749
2006	27.81377
2007	27.43868
2008	27.66239
2009	27.08286
2010	27.05182
2011	27.48698
2012	27.67992
2013	27.32305
2014	27.33634
2015	26.51131
2016	26.02547
2017	25.2691