Year	Percent
1960	15.4882
1961	15.48386
1962	14.19752
1963	18.2336
1964	19.1646
1965	20.91504
1966	22.03389
1967	23.33333
1968	21.86979
1969	21.2644
1970	21.08264
1971	22.56021
1972	20.33096
1973	20.19868
1974	33.13566
1975	26.53061
1976	20.47297
1977	19.47644
1978	22.7957
1979	25.2504
1980	24.78134
1981	22.48566
1982	23.37037
1983	21.41878
1984	20.20395
1985	21.66423
1986	19.86935
1987	19.97869
1988	21.54925
1989	24.31883
1990	22.5285
1991	25.15557
1992	23.77305
1993	20.67681
1994	21.22767
1995	22.18073
1996	21.06049
1997	20.12328
1998	16.86141
1999	16.20981
2000	18.31936
2001	17.15379
2002	18.39279
2003	18.41111
2004	17.14675
2005	17.18968
2006	18.42312
2007	18.68922
2008	18.17363
2009	15.98355
2010	16.17421
2011	17.62974
2012	18.43523
2013	18.66469
2014	17.26907
2015	17.65175
2016	16.98904
2017	16.84306