Year	Percent
1960	18.06369
1961	20.33547
1962	20.14885
1963	22.01518
1964	23.77788
1965	23.43812
1966	22.2124
1967	23.53558
1968	22.58421
1969	22.38219
1970	21.34359
1971	21.01872
1972	20.75119
1973	21.81348
1974	26.94639
1975	30.85317
1976	32.85801
1977	30.6275
1978	30.77986
1979	30.83046
1980	29.08648
1981	27.46275
1982	27.87529
1983	29.59491
1984	20.34754
1985	14.34682
1986	15.23715
1987	17.49887
1988	18.66821
1989	21.60044
1990	24.15114
1991	20.21833
1992	21.3384
1993	23.98137
1994	24.06281
1995	22.45052
1996	24.01583
1997	24.77576
1998	23.38636
1999	18.95822
2000	18.3676
2001	22.14143
2002	24.47046
2003	22.98049
2004	21.6116
2005	21.55041
2006	18.00905
2007	17.33734
2008	19.28806
2009	16.59156
2010	20.54072
2011	20.46625
2012	18.20364
2013	20.01602
2014	20.55345
2015	21.21436
2016	24.28321
2017	25.01717