Year	Percent
1964	13.0642
1965	14.39394
1966	18.61024
1967	20.17265
1968	20.04883
1969	19.37218
1970	24.39668
1971	23.91599
1972	22.3173
1973	25.81123
1974	25.75563
1975	18.13989
1976	20.24422
1977	23.72332
1978	29.78929
1979	18.13278
1980	24.50714
1981	22.91344
1982	21.86021
1983	20.92507
1984	19.81103
1985	25.32482
1986	21.76804
1987	24.28943
1988	25.44904
1989	24.86208
1990	24.16409
1991	20.97051
1992	16.92084
1993	17.61044
1994	19.29324
1995	21.81976
1996	15.00382
1997	15.14099
1998	16.69272
1999	15.52141
2000	17.41409
2001	18.79034
2002	15.13822
2003	16.48215
2004	16.9625
2005	17.64968
2006	18.63359
2007	20.45698
2008	19.61271
2009	19.33262
2010	20.8409
2011	21.70198
2012	21.5089
2013	20.10557
2014	22.43166
2015	21.46596
2016	17.29331
2017	19.27295