Year	Percent
1960	10.30928
1961	12.7506
1962	8.33333
1963	9.83125
1964	7.69231
1965	13.97193
1966	17.41935
1967	13.51075
1968	16.10377
1969	18.37472
1970	25.73317
1971	19.16996
1972	24.39324
1973	22.39011
1974	27.32394
1975	33.7172
1976	26.25817
1977	24.68407
1978	38.44136
1979	30.23713
1980	24.74381
1981	17.62476
1982	21.40334
1983	22.7975
1984	12.87923
1985	18.58707
1986	12.46993
1987	17.27067
1988	21.41806
1989	24.55677
1990	23.04047
1991	20.23571
1992	19.93461
1993	15.17123
1994	29.09818
1995	17.39214
1996	12.32709
1997	11.59881
1998	13.46502
1999	14.65001
2000	13.5647
2001	14.89653
2002	12.3036
2003	12.92234
2004	13.75469
2005	17.09475
2006	20.01404
2007	23.06913
2008	23.22912
2009	24.46289
2010	22.82319
2011	12.42477
2012	12.04941
2013	12.70246
2014	11.98556
2015	12.22162
2016	10.78028
2017	13.43222